gremlin vs sandman

gremlin and sandman both are nouns.

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

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

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

Other hyponyms of gremlin include leprechaun.

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