mid-14c., "deception, trick, device," of uncertain origin, probably from a Low German word meaning "a sharp sounding blow" (compare Middle English knak, late 14c.; German knacken "to crack"), of imitative origin. Sense of "special skill" is first recorded 1580s, if this is in fact the same word. In old slang (mid-18c.-mid-19c.) nacky meant "full of knacks; ingenious, dexterous."