A pointed device worn on a rider's heel to urge a horse forward; also any stimulus or incentive that prompts action or development.
From Old English 'spora', related to 'spurn' meaning to kick. The metaphorical sense of 'stimulus' developed from the literal use of spurs to motivate horses, extending to any driving force or incentive by the 14th century.
The phrase 'on the spur of the moment' reflects how spurs provide immediate motivation - just as a horse responds instantly to spurs, these decisions happen without planning. Spurs have been symbols of knighthood and horsemanship across cultures for over 2,000 years.
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