Rancor is bitter, long-lasting anger or resentment toward someone. It's not the quick flash of anger you feel when your brother takes your favorite seat: it's the kind of anger that sticks around, sometimes for years, poisoning how you think about a person.

Imagine two classmates who were once best friends but had a terrible argument. If one holds onto that anger month after month, refusing to forgive or let it go, that's rancor. The word suggests something deeper and more stubborn than ordinary anger: a festering bitterness that colors every interaction.

You might see rancor between rival teams whose fans can't let go of past defeats, or between neighbors after a serious dispute. In stories, characters consumed by rancor often make themselves miserable, unable to move forward because they're trapped in old grievances.

Rancor is anger that's gone bad, turned sour inside someone. While brief anger can be healthy and normal, rancor corrodes relationships and makes it impossible to see the person you're angry at clearly.