Source : Webster's Revised Unabridged Dictionary (1913)

Buckle \Buc"kle\, v. t. [imp. & p. p. {Buckled}; p. pr. & vb. n.
   {Buckling}.] [OE. boclen, F. boucler. See {Buckle}, n.]
   1. To fasten or confine with a buckle or buckles; as, to
      buckle a harness.

   2. To bend; to cause to kink, or to become distorted.

   3. To prepare for action; to apply with vigor and
      earnestness; -- generally used reflexively