sex gland vs testis

sex gland and testis both are nouns.

Word	Noun	Adjective	Verb	Adverb
sex gland	Yes	No	No	No
testis	Yes	No	No	No

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

sex gland: 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 sex gland include ovary, ovotestis, ball, ballock, bollock, egg, nut, orchis, testicle.

sex gland (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