testis vs gonad

testis and gonad both are nouns.

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

As nouns, gonad is a hypernym of testis; that is, gonad is a word with a broader meaning than testis:

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

Other hypernyms of testis include sex gland, male reproductive gland.

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