Feeble, but employed by business (6)
I believe the answer is:
infirm
'feeble' is the definition.
(I've seen this before)
'but employed by business' is the wordplay.
'but' becomes 'in' (I can't explain this - if you can you should believe this answer much more).
'employed by' says to put letters next to each other.
'business' becomes 'firm' (firm is a kind of business).
'in'+'firm'='INFIRM'
(Other definitions for infirm that I've seen before include "'Weak, ill (6)'" , "Weak and feeble" , "unstable" , "Feeble, decrepit" , "Frail" .)