Francophonie· medium
avoir les dents longues
“to have long teeth”
Meaning
to be ruthless about getting ahead
Explanation
The sense that stuck is a sharp hunger for money and standing, plus a willingness to walk over whoever is in the way. An older use, now more or less gone, meant being genuinely famished. It is not the English 'long in the tooth', which is about age and comes from a horse's receding gums.
Example
Le nouveau stagiaire a les dents longues, il veut déjà la place du directeur.
The new intern is ruthlessly ambitious, he's already eyeing the director's job.
Origin
Goes back to the 14th century, when it just meant being hungry. The hard, aggressive side of teeth pulled the sense across to ambition.
Source