singer vs tenor

singer and tenor both are nouns.

Word	Noun	Adjective	Verb	Adverb
singer	Yes	No	No	No
tenor	Yes	Yes	No	No

As nouns, tenor is a hyponym of singer; that is, tenor is a word with a more specific, narrower meaning than singer:

singer (noun)	tenor (noun)
a person who sings	the pitch range of the highest male voice
	the general meaning or substance of an utterance
	a settled or prevailing or habitual course of a person's life
	the adult male singing voice above baritone
	an adult male with a tenor voice

singer (adjective)	tenor (adjective)
	of or close in range to the highest natural adult male voice
	(of a musical instrument) intermediate between alto and baritone or bass