sleeping tablet vs tab

sleeping tablet and tab both are nouns.

Word	Noun	Adjective	Verb	Adverb
sleeping tablet	Yes	No	No	No
tab	Yes	No	No	No

As nouns, tab is a hypernym of sleeping tablet; that is, tab is a word with a broader meaning than sleeping tablet:

sleeping tablet: a soporific drug in the form of a pill (or tablet or capsule)
tab: a dose of medicine in the form of a small pellet

Other hypernyms of sleeping tablet include lozenge, pill, tablet, hypnotic, soporific.

sleeping tablet (noun)	tab (noun)
a soporific drug in the form of a pill (or tablet or capsule)	a dose of medicine in the form of a small pellet
	a short strip of material attached to or projecting from something in order to facilitate opening or identifying or handling it
	the key on a typewriter or a word processor that causes a tabulation
	the bill in a restaurant
	sensationalist journalism