copulation vs sexual relation

copulation and sexual relation both are nouns.

Word	Noun	Adjective	Verb	Adverb
copulation	Yes	No	No	No
sexual relation	Yes	No	No	No

As nouns, copulation and sexual relation are synonyms defined as:

copulation and sexual relation: sexual activity between individuals, especially the insertion of a man's penis into a woman's vagina until orgasm and ejaculation occur

copulation (noun)	sexual relation (noun)
sexual activity between individuals, especially the insertion of a man's penis into a woman's vagina until orgasm and ejaculation occur	sexual activity between individuals, especially the insertion of a man's penis into a woman's vagina until orgasm and ejaculation occur