sexual intercourse vs sexual relation

sexual intercourse and sexual relation both are nouns.

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

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

sexual intercourse 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

Other synonyms of sexual intercourse include carnal knowledge, coition, coitus, copulation, intercourse, relation, sex act, sexual congress.

sexual intercourse (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