Occasionally ignored threat of French business (5)
I believe the answer is:
trade
'business' is the definition.
(trade is a kind of business)
'occasionally ignored threat of french' is the wordplay.
'occasionally ignored' indicates alternate letters (ignore occasional letters and keep the rest).
'of french' becomes 'de' ('of' in French).
The alternating letters of 'threat' are 'tra'.
'tra'+'de'='TRADE'
(Other definitions for trade that I've seen before include "Customers" , "Deal - occupation" , "Transaction" , "Deal commercially" , "Business - deal" .)