Additional despatch cut by company (6)
I believe the answer is:
second
'additional' is the definition.
(I've seen this before)
'despatch cut by company' is the wordplay.
'despatch' becomes 'send' (I've seen this before).
'cut by' is an insertion indicator.
'company' becomes 'co' (abbreviation).
'send' going around 'co' is 'SECOND'.
(Other definitions for second that I've seen before include "A duellist's or boxer's assistant" , "Small fraction of a day" , "Moment in time" , "Silver medal position" , "another?" .)