Secretary at work is smart? (4)
I believe the answer is:
pain
'smart?' is the definition.
(smart is a kind of pain)
'secretary at work' is the wordplay.
'secretary' becomes 'pa' (abbreviation for personal assistant).
'at work' becomes 'in' (eg being in as opposed to being off sick).
'pa'+'in'='PAIN'
'is' acts as a link.
(Other definitions for pain that I've seen before include "French bread?" , "Mental distress" , "Unpleasant sensation" , "Tiresome figure" , "Suffering, distress" .)