bass horn vs brass instrument

bass horn and brass instrument both are nouns.

Word	Noun	Adjective	Verb	Adverb
bass horn	Yes	No	No	No
brass instrument	Yes	No	No	No

As nouns, brass instrument is a hypernym of bass horn; that is, brass instrument is a word with a broader meaning than bass horn:

bass horn: the lowest brass wind instrument
brass instrument: a wind instrument that consists of a brass tube (usually of variable length) that is blown by means of a cup-shaped or funnel-shaped mouthpiece

Other hypernyms of bass horn include bass, brass.

bass horn (noun)	brass instrument (noun)
the lowest brass wind instrument	a wind instrument that consists of a brass tube (usually of variable length) that is blown by means of a cup-shaped or funnel-shaped mouthpiece