The Spanish morder, “to bite”, sounds completely different than anything in English (except for obscure SAT words like mordant — which literally means, biting!).
But who would’ve thunk that it’s related to remorse.
Remorse comes from the Latin remordere, which means, “to bite back” — from the earlier re- (the prefix meaning “back” in this case) and mordere, from which we get, morder.
The remorseful do bite back indeed!