Occupied in wholesale trade (3)
I believe the answer is:
let
'occupied' is the definition.
(I've seen this in another clue)
'in wholesale trade' is the wordplay.
'in' indicates a hidden word.
'LET' can be found hidden inside 'wholesale trade'.
(Other definitions for let that I've seen before include "Allow the obstruction" , "Service that must be repeated" , "Rent out: grant" , "Allow on the tennis court" , "Allow; permit" .)