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early 15c., "very lively, frivolous," perhaps from Scandinavian base *skyt- (stem of Old Norse skjota "to shoot, launch, move quickly"), from PIE root *skeud- "to shoot, to chase, to throw, to project" (see shoot (v.)). Sense of "shy, nervous, apt to run" first recorded c.1500, of horses. Related: Skittishly; skittishness.