The Collaborative International Dictionary of English v.0.48:
Sear \Sear\, n. [F. serre a grasp, pressing, fr. L. sera. See Serry.] The catch in a gunlock by which the hammer is held cocked or half cocked. [1913 Webster] Sear spring, the spring which causes the sear to catch in the notches by which the hammer is held. [1913 Webster]