leprechaun vs brownie

leprechaun and brownie both are nouns.

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

As nouns, brownie is a hypernym of leprechaun; that is, brownie is a word with a broader meaning than leprechaun:

Other hypernyms of leprechaun include elf, gremlin, hob, imp, pixie, pixy.

leprechaun (noun)	brownie (noun)
a mischievous elf in Irish folklore	square or bar of very rich chocolate cake usually with nuts
	(folklore) fairies that are somewhat mischievous