'parallel' originates from Greek, specifically the word 'parállēlos' (παράλληλος), where 'para-' meant 'beside' and 'allēlos' meant 'one another'.

'parallel' changed from Greek 'parállēlos' into Late Latin 'parallellus', passed into Old French as 'paralel' and eventually became the modern English word 'parallel' in Middle English.

Initially, it meant 'lying side by side' (literally 'beside one another'); over time the meaning broadened but has largely remained 'side by side at equal distance' and extended metaphorically to 'similar' or 'analogous'.