also destrer, "riding horse of a noble breed, war horse," c. 1300, from Old French destrer, destrier (12c.), from Vulgar Latin *dextrarius "led by the right hand," from Latin dextra, fem. of dexter "right (hand)" (from PIE root *deks- "right; south"). So called because it was led at the right hand until wanted in battle. The spelling destrer was usual in Middle English; destrier was used later, in deliberately archaic or historic contexts.