Merriam-Webster's Collegiate® Dictionary, 11th Edition
SPUR
I. noun see: spurn Date: before 12th century
1. a pointed device secured to a rider's heel and used to urge on the horse, recognition and reward for achievement , a goad to action ; stimulus , something projecting like or suggesting a spur: as, a projecting root or branch of a tree, shrub, or vine, b. a stiff sharp spine (as on the wings or legs of a bird or insect), a gaff for a gamecock, a hollow projecting appendage of a corolla or calyx (as in larkspur or columbine), a bony outgrowth (as on the heel of the foot), climbing iron ,
4. an angular projection, offshoot, or branch extending out beyond or away from a main body or formation, a railroad track that branches off from a main line, a reinforcing buttress of masonry in a fortification, see: motive
II. verb (spurred; spurring)
Date: 13th century
transitive verb to urge (a horse) on with spurs, to incite to action or accelerated growth or development ; stimulate , to put spurs on, intransitive verb to spur one's horse on