PMS vs premenstrual syndrome

PMS and premenstrual syndrome both are nouns.

Word	Noun	Adjective	Verb	Adverb
PMS	Yes	No	No	No
premenstrual syndrome	Yes	No	No	No

As nouns, PMS and premenstrual syndrome are synonyms defined as:

PMS and premenstrual syndrome: a syndrome that occurs in many women from 2 to 14 days before the onset of menstruation

PMS (noun)	premenstrual syndrome (noun)
a syndrome that occurs in many women from 2 to 14 days before the onset of menstruation	a syndrome that occurs in many women from 2 to 14 days before the onset of menstruation