testis vs testicle

testis and testicle both are nouns.

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

As nouns, testis and testicle are synonyms defined as:

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

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

testis (noun)	testicle (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