Of the lower back (6)
I believe the answer is:
lumbar
'of the lower back' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for lumbar that I've seen before include "Area of the back between lowest ribs and pelvis" , "Relating to the lower backR" , "Relating to the back between lowest ribs and pelvis" , "Area of the back between lower ribs and pelvis" , "Near the part of the back between the ribs and the hipbones" .)