Agreement to fulfil orders with the Italian firm (5)
I believe the answer is:
wilco
'agreement to fulfil orders' is the definition.
(radio term short for 'will comply')
'with the italian firm' is the wordplay.
'with' becomes 'w' (abbreviation).
'the italian' becomes 'il' (the in Italian).
'firm' becomes 'co' (a firm is a company).
'w'+'il'+'co'='WILCO'
(Other definitions for wilco that I've seen before include "Term of agreement (in radio communication)" , "Radio comms expression of compliance" , "expression of agreement" , "Agreed (radio comms)" , "Roger might be followed by this" .)