sleeping pill vs pill

sleeping pill and pill both are nouns.

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

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

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

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

sleeping pill (noun)	pill (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
	something that resembles a tablet of medicine in shape or size
	a contraceptive in the form of a pill containing estrogen and progestin to inhibit ovulation and so prevent conception
	something unpleasant or offensive that must be tolerated or endured
	a unpleasant or tiresome person