bell tower vs tower

bell tower and tower both are nouns.

Word	Noun	Adjective	Verb	Adverb
bell tower	Yes	No	No	No
tower	Yes	No	Yes	No

As nouns, tower is a hypernym of bell tower; that is, tower is a word with a broader meaning than bell tower:

bell tower: a tower that supports or shelters a bell
tower: a structure taller than its diameter; can stand alone or be attached to a larger building

bell tower (noun)	tower (noun)
a tower that supports or shelters a bell	a structure taller than its diameter; can stand alone or be attached to a larger building
	anything that approximates the shape of a column or tower
	a powerful small boat designed to pull or push larger ships

bell tower (verb)	tower (verb)
	appear very large or occupy a commanding position