Unforgivable describes an action so terrible or hurtful that the person who was wronged finds it impossible to forgive. When someone does something unforgivable, they've crossed a line so serious that the relationship may never recover.

What makes an action unforgivable varies from person to person. One friend might forgive another for forgetting their birthday, but consider it unforgivable if that friend deliberately spread hurtful rumors. A teacher might forgive a student for turning in homework late, but consider cheating on a major test unforgivable.

The word suggests a betrayal of trust so deep that simply saying “I'm sorry” cannot fix it. If a teammate purposely sabotaged your science fair project after months of work together, you might feel their actions were unforgivable. If someone revealed a secret you specifically asked them to keep, knowing it would hurt you, that breach of trust might feel unforgivable.

Sometimes people use unforgivable to emphasize how wrong something is, even if they might eventually forgive it. A parent might say “What you did was unforgivable” to show how seriously disappointed they are, even though they still love their child and may still choose to forgive them.