undescended testicle vs testis

undescended testicle and testis both are nouns.

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

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

undescended testicle: a testis that fails to move into the scrotum as the male fetus develops
testis: one of the two male reproductive glands that produce spermatozoa and secrete androgens

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

undescended testicle (noun)	testis (noun)
a testis that fails to move into the scrotum as the male fetus develops	one of the two male reproductive glands that produce spermatozoa and secrete androgens