Uncontrollable means impossible to control, manage, or restrain. When something is uncontrollable, it keeps happening or growing no matter what you do to stop it.

A fit of uncontrollable giggles might hit you during a serious moment, when you know you should be quiet but the laughter just keeps bubbling up. A wildfire becomes uncontrollable when it spreads so fast and burns so hot that firefighters can't contain it. An uncontrollable dog pulls on its leash and ignores every command its owner gives.

The word often describes strong forces, emotions, or situations that have gotten beyond anyone's ability to manage. A rumor might spread through school in an uncontrollable way, reaching everyone before the truth has a chance to catch up. Sometimes fear or anger can feel uncontrollable, overwhelming your usual ability to stay calm.

Uncontrollable is stronger than simply “difficult to control.” It means that efforts to control something have failed or would fail. When scientists describe a disease outbreak as uncontrollable, they mean it's spreading despite their best efforts to stop it.