water sprite vs fay

water sprite and fay both are nouns.

Word	Noun	Adjective	Verb	Adverb
water sprite	Yes	No	No	No
fay	Yes	No	No	No

As nouns, fay is a hypernym of water sprite; that is, fay is a word with a broader meaning than water sprite:

Other hypernyms of water sprite include faerie, faery, fairy, sprite.

water sprite (noun)	fay (noun)
a fairy that inhabits water	a small being, human in form, playful and having magical powers
aquatic fern of tropical America often used in aquariums