coitus (n.)

"copulation," 1713, scientific Latin, from Latin coitus "a meeting together; sexual union," past participle of coire, from com- "together" (see co-) + ire (past participle itus) "come, go," (from PIE root *ei- "to go"). In Middle English as coite (early 15c.). Used in English in general senses of "meeting, uniting," and also of magnetic force, planetary conjunction, etc., before sexual sense came to predominate.