pixie vs leprechaun

pixie and leprechaun both are nouns.

Word	Noun	Adjective	Verb	Adverb
pixie	Yes	No	No	No
leprechaun	Yes	No	No	No

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

Other hyponyms of pixie include sandman.

pixie (noun)	leprechaun (noun)
(folklore) fairies that are somewhat mischievous	a mischievous elf in Irish folklore
creeping evergreen shrub having narrow overlapping leaves and early white star-shaped flowers; of the pine barrens of New Jersey and the Carolinas