C - Chaos, Criteria, Crystal, Cyan, Cynic, Cycle, Cyclone, Cylinder, Center, Cord, Card, Clone, Cardiac.

Chaos. From Ancient Greek χάος, khaos, vast chasm, void. A condition or place of great disorder or confusion.

Derived or related words: chaotic, chaotically.

Criteria. The plural form of criterion, formed according to the Ancient Greek  κριτήριον, kriterion, a test, a means of judging. From κριτής, krites, a judge. From κρίνω, krinō, I judge.

Derived or related words: criterion.

Crystal. From Ancient Greek κρύσταλλος, krestallos, ice. From κρύος, kreos, frost. A piece of glimmering, shining mineral resembling ice or glass.

Derived or related words: crystalline, crystallite, crystallization, crystallize, crystalloid.

Cyan. From Ancient Greek κύανος, kyanos, dark blue, dark blue enamel. A greenish blue, one of the subtractive primary.

Derived or related words: cyanide, cyanogen, cyanosis, cyanotic.

Cynic. From Ancient Greek κυνικός, kynikós, originally derived from the portico in Athens called Κυνόσαργες, Kynosarges. Of or relating to the belief that human actions are motivated only or primarily by base desires or selfishness. Skeptical of the integrity, sincerity, or motives of others.

Derived or related words: cynical, cynicism, cynically.

Cycle. From Ancient Greek κύκλος, kyklos, circle. An interval of space or time in which one set of events or phenomena is completed. A complete rotation of anything.
(Also recycle. From re-, again and‎ cycle, see above. To break down and reuse component materials.)

Derived or related words: cyclic, cyclone, cyclist, bicycle, tricycle.

Cyclone. From Ancient Greek κυκλώνω, kyklono, to completely rotate. From κύκλος, kyklos, circle. A system of winds rotating around a center of low atmospheric pressure.

Derived or related words: cyclonic.

Cylinder. From Ancient Greek κύλινδρος, kylindros. From κυλίνδειν, to roll. A surface created by projecting a closed two-dimensional curve along an axis intersecting the plane of the curve.

Derived or related words: cylindrical, cylindrically.

Center. From Ancient Greek κέντρον, kéntron. From κεντεῖν, to prick, goad. The point in the interior of a circle or sphere that is equidistant from all points on the circumference.

Derived or related words: centered, centering, central, centrally. 

Cord. From Ancient Greek χορδά, khorda, Ionic χορδή, khorde, string of gut, the string of a lyre. Also, a small flexible electrical conductor composed of wires insulated separately or in bundles and assembled together usually with an outer cover.

Derived or related words: cordial, cordially.

Card. From Ancient Greek χάρτης, chartēs, paper, papyrus. Any flat, normally rectangular piece of stiff paper, plastic etc.

Derived or related words: cardboard, postcard etc.

Clone. From Ancient Greek κλών, klōn, twig. A living organism (originally a plant) produced asexually from a single ancestor, to which it is genetically identical.

Derived or related words: cloning.

Cardiac. From Ancient Greek καρδιακός, kardiakos. From καρδιά, kardia, heart. Relating to the heart.

Derived or related words: cardiology, myocardial, pericardium.
 

M - Melody, Music, Muses, Muscle, Mathematics, Melancholy.

A melodic, mathematical post. Enjoy the knowledge!

Melody. From Ancient Greek μελῳδία, melōdiā, singing, chanting. From μέλος, mélos, member, part of a group + ἀοιδή, aoidḗ, song, contracted form ᾠδή, ōidḗ. A pleasing succession or arrangement of sounds.

Derived or related words: melodic, melodious, melodiously, melodiousness.
 

Music. From Ancient Greek μουσική, mousike, art of the Muses.

Derived or related words: musical.

 

Muses. From Ancient Greek αἱ μοῦσαι, hai moũsai, in Greek mythology, poetry, and literature, are the goddesses who inspire the creation of literature and the arts. They were considered the source of the knowledge, related orally for centuries in the ancient culture, that was contained in poetic lyrics and myths. The nine muses were: Clio, Thalia, Erato, Euterpe, Polyhymnia, Calliope, Terpsichore, Urania, Melpomene.

Muscle. From Ancient Greek μῦς, mus, mouse, muscle, mussel because of the mouse like appearance of some muscles. A tissue composed of fibers capable of contracting to effect bodily movement.

Derived or related words: musculus, muscular.

 

Mathematics. From Ancient Greek μαθηματικός, mathematikos, fond of learning. From μάθημα, máthema, knowledge, study, learning.

Derived or related words: mathematical, mathematically.

Melancholy. From Ancient Greek μελαγχολία, melancholia, atrabiliousness. From μέλας, melas, μελαν-, melan-, black, dark, murky + χολή, chole, bile.

Derived or related words: melancholic.

Medical terms

You should know all medical terms come from Ancient Greek and Latin. But the scientific word for each and most of them, which is used among doctors, medical schools and universities, is Greek. Of course I'm not capable of writing down the entire medical vocabulary but I will give you a satisfying example. Bear with me.

Amnesia. From Ancient Greek α-, a-, not + μημνέσκειν, memneskein, to remember - ἀμνησία, amnēsia, forgetfulness.

 
Anesthesia. From Greek αν-, an-, without and αἴσθησις, aisthēsis, sensation. Loss of sensation induced by drugs. It's called general anesthesia when consciousness is lost and local anesthesia when only a specific area of the body is involved.
   

Arthritis. From Greek άρθρο, joint and -ίτις. Inflammation of a joint or joints causing pain and/or disability , swelling and stiffness, and due to various causes such as infection, trauma, degenerative changes or metabolic disorders.

Bradycardia. From Ancient Greek βραδύς, vrades, slow and καρδιά, kardia, heart. Slowness of the heart rate.

Cardiology. From Greek καρδίᾱ, kardiā, heart and -λογία, -logia, the study of something, so the study of the heart.

Cancer. From Ancient Greek καρκίνος, karkinos , crab; applied to cancerous tumors because the enlarged veins resembled the legs of a crab.

Glaucoma. From Greek γλαύκωμα, glaukōma, an opacity of the crystalline lens, derived from γλαυκός, glaukós, clear. A disease of the eye in which pressure within the eyeball damages the optic disc, impairing vision, sometimes progressing to blindness.

Gynecology. From Ancient Greek γυνή, gyne, modern Greek γυναίκα, gynaika, woman and -λογία, study. So gynecology is the medical study of women. 

Orthodontics. From Greek ορθός, orthos, straight or proper or perfect and οδούς, odous, tooth. The dental specialty and practice of preventing and correcting irregularities of the teeth, as by the use of braces.

Osteoporosis. From Greek οστούν, ostoun, bone and πόρος, poros, pore is a disease of bones that leads to an increased risk of fracture. 

Paraplegia. From Ancient Greek παρά, beside and πλήσσειν, plessein, to strike. A condition where the lower half of a patient's body is paralyzed and cannot move.

Rhinoplasty. From Ancient Greek ῥις rhis, nose and πλάσσειν, plassein, to shape. Known as a nose job.
 

Stethoscope. From Greek στήθος, stéthos, chest and σκοπή, skopé, examination. It's an acoustic medical device for listening to the internal sounds of a body.


 

Thorax. From Greek θώραξ, thorax, breastplate. It's a division of a body that lies between the head and the abdomen.

H - Hour, Harmony, Horizon, Hormone.

Some Greek words beginning with the letter H:

Hour. From Ancient Greek ὥρα, hōrā, any time or period, whether of the year, month, or day.

Derived or related words: hourly.

Harmony. From Ancient Greek ἁρμονία, harmonia, joint, union, agreement, concord of sounds.

Derived or related words: harmonic, harmonious, harmonize, harmoniously.

Horizon. From Ancient Greek ὁρίζων κύκλος, horizōn kyklos, separating circle. From the verb ὁρίζω, horizō, to divide, to separate and that from ὅρος, oros, boundary, landmark.

Derived or related words: horizontal, horizontally. 

Hormone. From Ancient Greek ὁρμή, horme, rapid motion forwards, onrush, onset, assault, impulse to do a thing, effort. From ὁρμῶ, hormo, to set in motion, to urge on, to cheer on, to make a start.

Derived or related words: hormonal.

...(o)logy

Every word with two compounds, the second being -(o)logy, is Greek and means a study of a particular subject, something said, or a way of speaking . Some of them are:

Biology. From Ancient Greek βίος, bíos, bio-, life + -λογία, -logía, -logy, branch of study, to speak. The study of all life or living matter.

Geology. From Ancient Greek γῆ, gē, earth + -logia, -logy. The science that studies the structure of the earth (or other planets), together with its origin and development, especially by examination of its rocks.

Genealogy. From Ancient Greek γενεαλογία, genealogia, from γενεά, genea, generation, descent and -λογία, -logia, study of. The study of families and the tracing of their lineages and history.

Trilogy. From Ancient Greek τρεῖς, treis, three + λόγος, logos, story, account. A three-part series.

Apology. From Ancient Greek ἀπολογία, apologia, a speech in defense, from ἀπολογοῦμαι, apologoumai, I speak in one's defense, from ἀπό, apo, from, off + λόγος, logos, speech.

Anthropology. From Ancient Greek ἄνθρωπος, anthropos, man, mankind, human, humanity + -logy. The holistic scientific and social study of humanity.

Para... - Parallel, Paragraph, Parasite, Parameter, Paralysis.

Parallel. From Ancient Greek παράλληλος, from παρά, para, beside + ἄλληλος, allelos, along each other. Equally distant from one another at all points.

Paragraph. From Ancient Greek παράγραφος from παρά, para, beside + γράφω, grapho, I write.

Parasite. From Ancient Greek παράσιτος, parasitos, person who eats at the table of another, from noun use of adjective meaning feeding beside, from παρά, para, beside + σῖτος, sitos, food.

 

Parameter. From Ancient Greek παράμετρος, parametros, from παρά, para, beside + μέτρον, measure. A variable kept constant during an experiment, calculation or similar.

 Paralysis. From Ancient Greek παράλυσις, paralusis, palsy, from παραλύειν, paraluein, to disable on one side, from παρά, para, beside + λύειν, luein, loosen. The complete loss of voluntary control of part of person's body, such as one or more limbs.

P - Psychology, Psychopathy, Psychotherapy, Psychoanalysis.

Every word with two compounds, the first being Psycho-, is Greek and means something that has to do with the soul. Some examples:

Psychology. From Ancient Greek ψυχή, psukhē, soul + -logia, study of something.

Psychopathy. From Ancient Greek ψυχή, psukhē, soul +  πάθος, pathos, suffering.

Psychotherapy. From Ancient Greek ψυχή, psukhē, soul + θεραπεία, therapia, service, medical treatment, from θεραπεύω, therapeuō, I serve, treat medically.

Psychoanalysis. From Ancient Greek ψυχή, psukhē, soul + ἀνάλυσις, analisis, from ἀναλύω, analiō, I unravel, investigate.