lumbago (n.) Look up lumbago at Dictionary.com
1690s, from Late Latin lumbago "weakness of loins and lower back," from Latin lumbus "loin" (usually plural), from PIE *lendh- "loin" (cognates: Old Church Slavonic ledvije (plural) "loins; soul," Russian ljadveja "loin;" Old English lendenu "loins," German Lende "loin," Lenden "loins").