hubby vs househusband

hubby and househusband both are nouns.

Word	Noun	Adjective	Verb	Adverb
hubby	Yes	No	No	No
househusband	Yes	No	No	No

As nouns, househusband is a hyponym of hubby; that is, househusband is a word with a more specific, narrower meaning than hubby:

hubby: a married man; a woman's partner in marriage
househusband: a husband who keeps house while his wife earns the family income

Other hyponyms of hubby include benedick, benedict, cuckold, family man, house husband, uxoricide.

hubby (noun)	househusband (noun)
a married man; a woman's partner in marriage	a husband who keeps house while his wife earns the family income