A traitor is someone who betrays their country, group, or cause by helping its enemies or breaking their loyalty in a serious way. The word carries strong disapproval because it describes someone who turns against people who trusted them.

In wartime, a traitor might share military secrets with the enemy or help them attack. Benedict Arnold became America's most famous traitor during the Revolutionary War when he plotted to surrender West Point to the British, even though he had been a trusted general in the Continental Army. Throughout history, countries have treated treason (the act of being a traitor) as one of the most serious crimes.

The word appears in smaller contexts too. You might hear someone jokingly called a traitor for switching to root for a rival sports team, or for revealing the ending of a movie their friends haven't seen yet. But these casual uses don't carry the same weight as the original meaning.

What makes someone a traitor is secretly working against people who counted on their loyalty, sometimes for personal gain or out of cowardice. The disgrace comes from the sneaky betrayal of trust when it matters most, not from having different opinions or changing your mind openly.