sex act vs sexual intercourse

sex act and sexual intercourse both are nouns.

Word	Noun	Adjective	Verb	Adverb
sex act	Yes	No	No	No
sexual intercourse	Yes	No	No	No

As nouns, sex act and sexual intercourse are synonyms defined as:

sex act 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

sex act (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