countertenor vs singing voice

countertenor and singing voice both are nouns.

Word	Noun	Adjective	Verb	Adverb
countertenor	Yes	Yes	No	No
singing voice	Yes	No	No	No

As nouns, singing voice is a hypernym of countertenor; that is, singing voice is a word with a broader meaning than countertenor:

countertenor (noun)	singing voice (noun)
the highest adult male singing voice	the musical quality of the voice while singing
a male singer with a voice above that of a tenor

countertenor (adjective)	singing voice (adjective)
of or being the highest male voice; having a range above that of tenor