imp vs nipper

imp and nipper both are nouns.

Word	Noun	Adjective	Verb	Adverb
imp	Yes	No	No	No
nipper	Yes	No	No	No

As nouns, nipper is a hypernym of imp; that is, nipper is a word with a broader meaning than imp:

Other hypernyms of imp include child, fry, kid, minor, nestling, shaver, small fry, tiddler, tike, tyke, youngster.

imp (noun)	nipper (noun)
one who is playfully mischievous	a grasping structure on the limb of a crustacean or other arthropods
(folklore) fairies that are somewhat mischievous	a young person of either sex