sandman vs elf

sandman and elf both are nouns.

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

As nouns, elf is a hypernym of sandman; that is, elf 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
elf: (folklore) fairies that are somewhat mischievous

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

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