1690s, from Late Latin lumbago "weakness of loins and lower back," from Latin lumbus "loin" (usually plural), from PIE *lendh- "loin" (cf. Old Church Slavonic ledvije (plural) "loins; soul," Russian ljadveja "loin;" Old English lendenu "loins," German Lende "loin," Lenden "loins").
lumbago lum·ba·go (lŭm-bā'gō)
A painful condition of the lower back, as one resulting from muscle strain or a slipped disk. Also called lumbar rheumatism.