Avoir une dent contre quelqu'un translates as feeling angry or resentful towards someone.
Literally, avoir une dent contre means ‘to have a tooth against’.
This expression dating from the 14th century evolved from avoir les dents sur quelqu’un – to have your teeth on someone.
As there were no dentists in the modern sense in the 14th century, just ‘tooth pullers’, teeth at the time were commonly associated with pain.
But in this expression, they are a symbol of aggression.
After all, if you have your teeth on someone it is quite possible that you’ve just bitten them.
Some sources also say the expression may also be linked to the idea of animals ‘showing their teeth’ when they are in an aggressive mood.
By the 17th century, the expression had evolved to just une dent, one tooth, though it is unclear why.
One variant found in Molière, but not used today, was avoir une dent de lait (a young child’s ‘baby’ tooth) contre quelqu’un to refer to a longstanding grudge.