sniveller vs unpleasant person

sniveller and unpleasant person both are nouns.

Word	Noun	Adjective	Verb	Adverb
sniveller	Yes	No	No	No
unpleasant person	Yes	No	No	No

As nouns, unpleasant person is a hypernym of sniveller; that is, unpleasant person is a word with a broader meaning than sniveller:

Other hypernyms of sniveller include disagreeable person.

sniveller (noun)	unpleasant person (noun)
a person given to excessive complaints and crying and whining	a person who is not pleasant or agreeable