Spur  —n. 1 small spike or spiked wheel worn on a rider's heel for urging on a horse. 2 stimulus, incentive. 3 spur-shaped thing, esp.: a a projection from a mountain or mountain range. B a branch road or railway. C a hard projection on a cock's leg. —v. (-rr-) 1 prick (a horse) with spurs. 2 incite or stimulate.  on the spur of the moment on impulse. [old english]