sandman vs pixie

sandman and pixie both are nouns.

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

As nouns, pixie is a hypernym of sandman; that is, pixie is a word with a broader meaning than sandman:

sandman: an elf in fairy stories who sprinkles sand in children's eyes to make them sleepy
pixie: (folklore) fairies that are somewhat mischievous

Other hypernyms of sandman include brownie, elf, gremlin, hob, imp, pixy.

sandman (noun)	pixie (noun)
an elf in fairy stories who sprinkles sand in children's eyes to make them sleepy	(folklore) fairies that are somewhat mischievous
	creeping evergreen shrub having narrow overlapping leaves and early white star-shaped flowers; of the pine barrens of New Jersey and the Carolinas