pimple vs pustule

pimple and pustule both are nouns.

Word	Noun	Adjective	Verb	Adverb
pimple	Yes	No	No	No
pustule	Yes	No	No	No

As nouns, pustule is a hyponym of pimple; that is, pustule is a word with a more specific, narrower meaning than pimple:

pimple: a small inflamed elevation of the skin; a pustule or papule; common symptom in acne
pustule: a small inflamed elevation of skin containing pus; a blister filled with pus

Other hyponyms of pimple include papule.

pimple (noun)	pustule (noun)
a small inflamed elevation of the skin; a pustule or papule; common symptom in acne	a small inflamed elevation of skin containing pus; a blister filled with pus