Contractor told to purchase mushrooms (6)
I believe the answer is:
biceps
'contractor' is the definition.
(I've seen this before)
'told to purchase mushrooms' is the wordplay.
'told' shows a homophone (sound like).
'to purchase' becomes 'buy' (buy is a kind of purchase).
'mushrooms' becomes 'ceps' (cep is a type of mushroom).
'buy' is a homophone of 'bi'.
'bi'+'ceps'='BICEPS'
(Other definitions for biceps that I've seen before include "Arm workers" , "Type of muscle" , "Weightlifters use them" , "Large upper arm muscle" , "Elbow-bending muscle" .)