tub vs hip bath

tub and hip bath both are nouns.

Word	Noun	Adjective	Verb	Adverb
tub	Yes	No	No	No
hip bath	Yes	No	No	No

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

tub: a relatively large open container that you fill with water and use to wash the body
hip bath: a bathtub in which your buttocks and hips are immersed as if you were sitting in a chair and you bathe in a sitting position

Other hyponyms of tub include footbath, hot tub, sitz bath.

tub (noun)	hip bath (noun)
a large open vessel for holding or storing liquids	a bathtub in which your buttocks and hips are immersed as if you were sitting in a chair and you bathe in a sitting position
a relatively large open container that you fill with water and use to wash the body
the amount that a tub will hold