To vacillate means to waver back and forth between different opinions or actions, unable to make a firm decision. When you vacillate, you keep changing your mind: first you want pizza for dinner, then tacos, then back to pizza, then maybe pasta instead.

The word captures that frustrating feeling of being stuck between choices. A student might vacillate between joining the soccer team or the drama club, spending days going back and forth without committing to either. A character in a story might vacillate between telling the truth or keeping a secret, their uncertainty creating tension in the plot.

Vacillating is different from simply thinking carefully. When you deliberate, you're weighing options thoughtfully before deciding. When you vacillate, you're spinning your wheels, unable to settle on an answer even after considering the choices. Someone who vacillates too much can frustrate friends and teammates who need a clear decision.

The word can suggest weakness or indecisiveness. In moments requiring courage or clarity, vacillating can mean missing an opportunity entirely.