Business I left is to wind (4)
I believe the answer is:
coil
'is to wind' is the definition.
(I've seen this in another clue)
'business i left' is the wordplay.
'business' becomes 'co' (short for company).
'left' becomes 'l' (common abbreviation).
'co'+'i'+'l'='COIL'
(Other definitions for coil that I've seen before include "Twist" , "Convolute" , "Wire winding" , "Wind in a series of loops" , "Wound length (of rope)" .)