sleeping capsule vs sleeping pill

sleeping capsule and sleeping pill both are nouns.

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

As nouns, sleeping capsule and sleeping pill are synonyms defined as:

sleeping capsule and sleeping pill: a soporific drug in the form of a pill (or tablet or capsule)

Other synonyms of sleeping capsule include sleeping draught, sleeping tablet.

sleeping capsule (noun)	sleeping pill (noun)
a soporific drug in the form of a pill (or tablet or capsule)	a soporific drug in the form of a pill (or tablet or capsule)