Classic dealings curtailed (4)
I believe the answer is:
'classic' is the definition.
(abbreviation of traditional)
'dealings curtailed' is the wordplay.
'dealings' becomes 'trade' (trade is a kind of dealings).
'curtailed' means to remove the last letter.
'trade' with its final letter removed is 'TRAD'.
(Other definitions for trad that I've seen before include "Classical (abbr)" , "Conventional (jazz)" , "music" , "Style of jazz" , "Form of folk or jazz" .)