SSRI vs antidepressant

SSRI and antidepressant both are nouns.

Word	Noun	Adjective	Verb	Adverb
SSRI	Yes	No	No	No
antidepressant	Yes	No	No	No

As nouns, antidepressant is a hypernym of SSRI; that is, antidepressant is a word with a broader meaning than SSRI:

SSRI: an antidepressant drug that acts by blocking the reuptake of serotonin so that more serotonin is available to act on receptors in the brain
antidepressant: any of a class of drugs used to treat depression; often have undesirable side effects

Other hypernyms of SSRI include antidepressant drug.

SSRI (noun)	antidepressant (noun)
an antidepressant drug that acts by blocking the reuptake of serotonin so that more serotonin is available to act on receptors in the brain	any of a class of drugs used to treat depression; often have undesirable side effects