sleeping tablet vs tablet

sleeping tablet and tablet both are nouns.

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

As nouns, tablet is a hypernym of sleeping tablet; that is, tablet 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)
tablet: a dose of medicine in the form of a small pellet

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

sleeping tablet (noun)	tablet (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 small flat compressed cake of some substance
	a slab of stone or wood suitable for bearing an inscription
	a portable computer with a touchscreen
	a number of sheets of paper fastened together along one edge