(1):

(v. t.) To express by grinning.

(2):

(n.) The act of closing the teeth and showing them, or of withdrawing the lips and showing the teeth; a hard, forced, or sneering smile.

(3):

(v. i.) To set the teeth together and open the lips, or to open the mouth and withdraw the lips from the teeth, so as to show them, as in laughter, scorn, or pain.

(4):

(v. i.) To show the teeth, as a dog; to snarl.

(5):

(n.) A snare; a gin.