Tic/tɪk/ Definition 1 of 3Pro Tip 1/3Involuntary Action A tic is an involuntary movement or sound that a person cannot control. Even during his presentation, his nervous tic appeared. Pro Tip 2/3Not Persistent Tics are usually temporary and could be caused by stress or tiredness. Her eye tic only shows up when she's exhausted. Pro Tip 3/3Medical Condition Frequent or severe tics can be a sign of a medical condition like Tourette syndrome. He was diagnosed with a condition that makes him have tics.