Old English swingan "to rush, fling oneself," from Proto-Germanic *swenganan (cf. Old Saxon, Old High German swingan, Old Frisian swinga, German schwingen "to swing, swingle, oscillate") denoting "violent circulatory motion." The meaning "move freely back and forth" is first recorded 1540s. Related: Swung; swinging. Swing shift first recorded 1941, typically 4 p.m. to midnight.