hi-fi vs high fidelity

hi-fi and high fidelity both are nouns.

Word	Noun	Adjective	Verb	Adverb
hi-fi	Yes	Yes	No	No
high fidelity	Yes	No	No	No

As nouns, hi-fi and high fidelity are synonyms defined as:

hi-fi and high fidelity: the reproduction of sound with little or no distortion

hi-fi (noun)	high fidelity (noun)
the reproduction of sound with little or no distortion	the reproduction of sound with little or no distortion
equipment for the reproduction of sound with high fidelity

hi-fi (adjective)	high fidelity (adjective)
characterized by minimal distortion in sound reproduction