Backache (7)
I believe the answer is:
lumbago
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">backache</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I know that lumbago is a type of backache)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for lumbago that I've seen before include "Rheumatic backache" , "Rheumatic pain in muscles of lower back" , "Back affliction" , "Back problem" , "Maul bog badly for a rheumatic affliction" .)