little theatre vs theater

little theatre and theater both are nouns.

Word	Noun	Adjective	Verb	Adverb
little theatre	Yes	No	No	No
theater	Yes	No	No	No

As nouns, theater is a hypernym of little theatre; that is, theater is a word with a broader meaning than little theatre:

little theatre: a small theater for experimental drama or collegiate or community groups
theater: a building where theatrical performances or motion-picture shows can be presented

Other hypernyms of little theatre include house, theatre.

little theatre (noun)	theater (noun)
a small theater for experimental drama or collegiate or community groups	a building where theatrical performances or motion-picture shows can be presented
	the art of writing and producing plays
	a region in which active military operations are in progress