gonad vs testicle

gonad and testicle both are nouns.

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

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

gonad: a gland in which gametes (sex cells) are produced
testicle: 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, testis.

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