Excessive ability holding doctor back (3,4)
I believe the answer is:
too much
'excessive' is the definition.
(I've seen this before)
'ability holding doctor back' is the wordplay.
'ability' becomes 'touch' (touch is a kind of ability).
'holding' indicates putting letters inside.
'doctor back' becomes 'om' (I can't justify this - if you can you should believe this answer much more).
'touch' enclosing 'om' is 'TOO MUCH'.
Can you help me to learn more?
(Other definitions for too much that I've seen before include "More than enough" , "More than is tolerable" , "American expression of approval" , "Excessive amount - far out!" , "Excess, more than is needed" .)