[Q] From Ron Ferguson: I just saw this on the Net and wondered if it was true: was the word testify based on men in the Roman court swearing to the truth of a statement on their testicles?
[A] I’ve seen that, too. This would seem as good a moment as any to scotch the story. There really is a strong link between testicle and testify (as well as attest, intestate, testament, contest and other words) but those who swear by this belief have misunderstood the matter.
The Latin word for a witness was testis, which derives from an Indo-European word for the number three. That was because the Romans regarded a witness as what we would call a trusted third party, one who stands aside from the dispute and can tell it how it really was.