testicle vs testis

testicle and testis both are nouns.

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

As nouns, testicle and testis are synonyms defined as:

testicle and testis: one of the two male reproductive glands that produce spermatozoa and secrete androgens

Other synonyms of testicle include ball, ballock, bollock, egg, nut, orchis.

testicle (noun)	testis (noun)
one of the two male reproductive glands that produce spermatozoa and secrete androgens	one of the two male reproductive glands that produce spermatozoa and secrete androgens