coitus (n.) Look up coitus at Dictionary.com
"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," (see ion). 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.