Meaning

noun a dull stupid fatuous person

noun an abrupt spasmodic movement

noun (mechanics) the rate of change of acceleration

originProbably from Middle English yerk (“sudden motion”) and Middle English yerkid (“tightly pulled”), from Old English ġearc (“ready, active, quick”) and Old English ġearcian (“to prepare, make ready, procure, furnish, supply”). Cognate with Scots yerk (“to jerk”). Related also to English yare (“ready”).

Etymology from Wiktionary, CC BY-SA 3.0