footbath vs tub

footbath and tub both are nouns.

Word	Noun	Adjective	Verb	Adverb
footbath	Yes	No	No	No
tub	Yes	No	No	No

As nouns, tub is a hypernym of footbath; that is, tub is a word with a broader meaning than footbath:

footbath: a small bathtub for warming or washing or disinfecting the feet
tub: a relatively large open container that you fill with water and use to wash the body

Other hypernyms of footbath include bathing tub, bathtub.

footbath (noun)	tub (noun)
a small bathtub for warming or washing or disinfecting the feet	a large open vessel for holding or storing liquids
	a relatively large open container that you fill with water and use to wash the body
	the amount that a tub will hold