The Collaborative International Dictionary of English v.0.48:
Lumbago \Lum*ba"go\, n. [L., fr. lumbus loin. See Lumbar.] (Med.) A rheumatic pain in the loins and the small of the back. [1913 Webster] LumbarWordNet (r) 3.0 (2006):
lumbago n 1: backache affecting the lumbar region or lower back; can be caused by muscle strain or arthritis or vascular insufficiency or a ruptured intervertebral disc [syn: lumbago, lumbar pain]