The word testicle was borrowed in 1704 so as to be a less vulgar way to describe male reproductive glands. This, as basically all gentrified words, come from Latin, but this case is far more interesting than most, as it's from the word testis, meaning "witness". This crazy connection came about because testicles were seen as "bearing witness to male virility" or "manliness". And, yes, for those wondering, this word is connected to the word testify (through Old French testifier and Middle English testifien, in conjunction with the verb facere, meaning "to make"). So, like felony, testify is a legal term with inappropriate connections. I wonder how many more lurk out there. Anyway, testis comes from the Proto-Indo-European tris, meaning "three", implying that a witness is an impartial third person. Interesting side note: testicle and testify are also connected to the word testament, through Latin testamentum, meaning "last will". This forms a sort of perfect etymological synergy between law, religion, and the human body.
Adam Aleksic, a freshman studying linguistics at Harvard University, has been described as the internet's sixth most famous etymologist. He has disturbing interests in words, vexillology, geography, board games, limericks, and law, and he loves writing about himself in the third person.
The Etymology Nerd