countertenor vs alto

countertenor and alto both are nouns.

Word	Noun	Adjective	Verb	Adverb
countertenor	Yes	Yes	No	No
alto	Yes	Yes	No	No

As adjectives, countertenor and alto are synonyms defined as:

countertenor and alto: of or being the highest male voice; having a range above that of tenor

As nouns, countertenor and alto are synonyms defined as:

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

countertenor (noun)	alto (noun)
the highest adult male singing voice	the pitch range of the lowest female voice
a male singer with a voice above that of a tenor	(of a musical instrument) the second highest instrument in a family of musical instruments
	the lowest female singing voice
	the highest adult male singing voice
	a singer whose voice lies in the alto clef

countertenor (adjective)	alto (adjective)
of or being the highest male voice; having a range above that of tenor	(of a musical instrument) second highest member of a group
	of or being the highest male voice; having a range above that of tenor
	of or being the lowest female voice