Tit for tat

This expression means like for like as in retaliation or reciprocation. There are two theories about its origin. Some sources maintain that it is a corruption of the French phrase, tant pour tant meaning so much for so much. Other sources, including the OED, maintain that it originated in the 15th century and started out as ‘tip for tap’ meaning that even a light blow, a tap, deserved another in retaliation. A century later, it had evolved or corrupted into tit for tat. Today, the expression has largely lost its original context of trading blows.