From The Collaborative International Dictionary of English v.0.48 :
Testis \Tes"tis\, n.; pl. Testes. [L.] (Anat.)
A testicle.
[1913 Webster]
From WordNet (r) 3.0 (2006) :
testis
n 1: one of the two male reproductive glands that produce
spermatozoa and secrete androgens; "she kicked him in the
balls and got away" [syn: testis, testicle, orchis,
ball, ballock, bollock, nut, egg]