sexual relation vs sexual intercourse

sexual relation and sexual intercourse both are nouns.

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

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

sexual relation and sexual intercourse: 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 relation include carnal knowledge, coition, coitus, copulation, intercourse, relation, sex act, sexual congress.

sexual relation (noun)	sexual intercourse (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