GP not fit for practice (5)
I believe the answer is:
drill
'for practice' is the definition.
(synonyms)
'gp not fit' is the wordplay.
'gp' becomes 'dr' (general practitioner).
'not fit' becomes 'ill' (I can't explain this - if you can you should give a lot more credence to this answer).
'dr'+'ill'='DRILL'
Can you help me to learn more?
(Other definitions for drill that I've seen before include "School" , "Stout cotton cloth" , "Dental assistant" , "Rehearsal; boring tool" , "Tool for boring holes" .)