Source : Webster's Revised Unabridged Dictionary (1913)

Lumbosacral \Lum`bo*sa"cral\, n. [L. lumbus loin + E. sacral.]
   (Anat.)
   Of or pertaining to the loins and sacrum; as, the lumbosacral
   nerve, a branch of one of the lumber nerves which passes over
   the sacrum.

Source : WordNet®

lumbosacral
     adj : of or relating to or near the small of the back and the back
           part of the pelvis between the hips