What does "tic" mean?

Tic: A local and habitual convulsive motion of certain muscles; especially, such a motion of some of the muscles of the face; twitching; velication; -- called also spasmodic tic. Dunglison. Tic douloureux (. Etym: [F., fr. tic a knack, a twitching + douloureux painful.] (Med.) Neuralgia in the face; face ague. See under Face.