sleeping capsule vs tablet

sleeping capsule and tablet both are nouns.

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

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

sleeping capsule: 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 capsule include lozenge, pill, tab, hypnotic, soporific.

sleeping capsule (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