1. ( pl. tetani) A powerful sustained contraction of a skeletal muscle resulting from the summation of a series of rapid muscular contractions (twitches) that are induced by repeated stimulation of the muscle.

2. A disease caused by the bacterium Clostridium tetani, which generally enters the body via an open wound. A toxin produced by the bacterium irritates the nerves, which induce muscle spasms that begin in the jaw muscles (giving the disease the informal name of lockjaw).