Since its first use centuries ago, fret has referred to an act of eating, especially when done by animals—in particular, small ones. You might speak, for example, of moths fretting your clothing. Like eat, fret also developed figurative senses to describe actions that corrode or wear away. A river could be said to "fret away" at its banks or something might be said to be "fretted out" with time or age. Fret can also be applied to emotional experiences so that something that "eats away at us" might be said to "fret the heart or mind." This use developed into the specific meaning of "vex" or "worry" with which we often use fret today.