Skittish

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late Middle English: perhaps from the rare verb skit ‘move lightly and rapidly’.

wiktionary

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Probably from skite(“to move lightly and hurriedly; to move suddenly, particularly in an oblique direction (Scotland, Northern England)”) +‎ -ish; compare skitter.

etymonline

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skittish (adj.)

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, chase, throw." Sense of "shy, nervous, apt to run" first recorded c. 1500, of horses. Related: Skittishly; skittishness.