bath vs bubble bath

bath and bubble bath both are nouns.

Word	Noun	Adjective	Verb	Adverb
bath	Yes	No	No	No
bubble bath	Yes	No	No	No

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

bath: a soaking and washing in a bathtub
bubble bath: a bath in which you add something to foam and scent the bath water

Other hyponyms of bath include mikvah, mud bath.

bath (noun)	bubble bath (noun)
a soaking and washing in a bathtub	a bath in which you add something to foam and scent the bath water
a vessel containing liquid in which something is immersed (as to process it or to maintain it at a constant temperature or to lubricate it)	a crystal, powder, or liquid preparation that foams in, scents, and softens bathwater.
an ancient Hebrew liquid measure equal to about 10 gallons