Western vs feature film

Western and feature film both are nouns.

Word	Noun	Adjective	Verb	Adverb
Western	Yes	No	No	No
feature film	Yes	No	No	No

As nouns, feature film is a hypernym of Western; that is, feature film is a word with a broader meaning than Western:

Western: a film about life in the western United States during the period of exploration and development
feature film: the principal (full-length) film in a program at a movie theater

Other hypernyms of Western include feature.

Western (noun)	feature film (noun)
a film about life in the western United States during the period of exploration and development	the principal (full-length) film in a program at a movie theater