hubby vs better half

hubby and better half both are nouns.

Word	Noun	Adjective	Verb	Adverb
hubby	Yes	No	No	No
better half	Yes	No	No	No

As nouns, better half is a hypernym of hubby; that is, better half is a word with a broader meaning than hubby:

Other hypernyms of hubby include adult male, man, married person, mate, partner, spouse.

hubby (noun)	better half (noun)
a married man; a woman's partner in marriage	a person's partner in marriage