It means to command someone not to do something.
1 : to proscribe from or as if from the position of one in authority : command against <the law forbids stores to sell liquor to minors> <her mother forbids her to go> 2 : to hinder or...
you forbid means that you do not allow
Vetere - to forbid.
ban prohibit disallow enjoin restrict bar
The four letter word that means, "I forbid," is veto. veto