detent

Detent \De*tent"\, n. [F. d['e]tente, fr. d['e]tendre to unbend, relax; pref. d['e]- (L. dis- or de) + tendre to stretch. See {Distend}.] (Mech.) That which locks or unlocks a movement; a catch, pawl, or dog; especially, in clockwork, the catch which locks and unlocks the wheelwork in striking. [1913 Webster]