whiplash n.

"instrument for flagellating," early 14c., from whip (v.) and perhaps in part from Middle Low German wippe "quick movement." In parliamentary use from 1850 (the verb in this sense is recorded from 1742), from the sense in fox-hunting. The parliamentary whip's duty originally was to ensure the attendance of party members on important occasions.

c. 1300, las "a blow, a stroke," later "flexible part of a whip" (late 14c.), possibly imitative; compare lash (v.1), which might be the immediate source of this. Century Dictionary says Irish lasg "a lash, whip, whipping" is of English origin. The lash "punishment by flogging" is from 1690s.