bellyacher vs unpleasant person

bellyacher and unpleasant person both are nouns.

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

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

Other hypernyms of bellyacher include disagreeable person.

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