Is it farther or further?
late 14c., "coupling," from Middle French copulation "mating, copulation" (14c.), from Latin copulationem (nominative copulatio), noun of action from past participle stem of copulare (see copulate). Of the sex act from late 15c., and this became the main sense from 16c.
copulation cop·u·la·tion (kŏp'yə-lā'shən)
Conjugation between two cells that do not fuse but separate after mutual fertilization.