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.