gonad vs testis

gonad and testis both are nouns.

Word	Noun	Adjective	Verb	Adverb
gonad	Yes	No	No	No
testis	Yes	No	No	No

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

gonad: a gland in which gametes (sex cells) are produced
testis: one of the two male reproductive glands that produce spermatozoa and secrete androgens

Other hyponyms of gonad include ovary, ovotestis, ball, ballock, bollock, egg, nut, orchis, testicle.

gonad (noun)	testis (noun)
a gland in which gametes (sex cells) are produced	one of the two male reproductive glands that produce spermatozoa and secrete androgens