testicle

Short definition from Wiktionary

Noun

1. 1
   A testis: the male sex and endocrine gland, found in most types of animals, that produces sperm and male sex hormones, including the steroid testosterone.
2. 2
   Either half of the structure that contains the testes: one side of the scrotum and its contents, considered as one object (one half of the ballsack, including its ball).