Английский Этимологический словарь - spur (n.)

- O.E. spura, spora (related to spurnan "to kick," see spurn), from P.Gmc. *spuron, from PIE *spere- "ankle." Generalized sense of "anything that urges on, stimulus," is from c.1390. The verb is c.1200, from the noun. "Widely extended senses ... are characteristic of a horsey race." [Weekley] On the spur of the moment preserves archaic on the spur "in great haste." To win one's spurs is to gain knighthood by some valorous act.