night bell vs doorbell

night bell and doorbell both are nouns.

Word	Noun	Adjective	Verb	Adverb
night bell	Yes	No	No	No
doorbell	Yes	No	No	No

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

night bell: a doorbell to be used at night
doorbell: a push button at an outer door that gives a ringing or buzzing signal when pushed

Other hypernyms of night bell include bell, buzzer.

night bell (noun)	doorbell (noun)
a doorbell to be used at night	a push button at an outer door that gives a ringing or buzzing signal when pushed