spur 
(spûr)
(spûr)n.
1. A short spike or spiked wheel that attaches to the heel of a rider's boot and is used to urge a horse forward.
2. An incentive: a spur to action.
3. A spurlike attachment or projection, as:
a. A spinelike process on the leg of some birds.
b. A climbing iron; a crampon.
c. A gaff attached to the leg of a gamecock.
d. A short or stunted branch of a tree.
e. A bony outgrowth or protuberance.
4. A lateral ridge projecting from a mountain or mountain range.
5. An oblique reinforcing prop or stay of timber or masonry.
6. Botany A tubular or saclike extension of the corolla or calyx of a flower, as in a columbine or larkspur.
7. An ergot growing on rye.
8. A spur track.
v. spurred, spur·ring, spurs
v.tr.
1. To urge (a horse) on by the use of spurs.
2. To incite or stimulate: "A business tax cut is needed to spur industrial investment" (New York Times).
v.intr.
To ride quickly by spurring a horse.
[Middle English spure, from Old English spura; see sperə- in the Appendix of Indo-European roots.]
spurtop: metal spurs
bottom: on a columbine flower
spur