Stabs in the back? (7)
I believe the answer is:
lumbago
'stabs in the back?' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.
'in the back?' is the wordplay.
'in the' becomes 'lumb' (I can't explain this - if you can you should give a lot more credence to this answer).
'back?' becomes 'ago' ('years back' means 'years ago').
'lumb'+'ago'='LUMBAGO'
Can you help me to learn more?
(Other definitions for lumbago that I've seen before include "Painful condition" , "Rheumatism of lower back" , "Back complaint" , "Rheumatic pain in muscles of lower back" , "Back problem" .)