The Collaborative International Dictionary of English v.0.48:

Lumbar \Lum"bar\, Lumbal \Lum"bal\, a. [L. lumbus loin. See
   Loin.] (Anat.)
   Of, pertaining to, or near, the loins; as, the lumbar
   arteries.
   [1913 Webster]

   Lumbar region (Anat.), the region of the loin;
      specifically, a region between the hypochondriac and iliac
      regions, and outside of the umbilical region.
      [1913 Webster]