Trade ban: almost board ship and depart (7)
I believe the answer is:
embargo
'trade ban' is the definition.
(I've seen this before)
'almost board ship and depart' is the wordplay.
'almost' means to remove the last letter (most of the word but not all of it).
'board ship' becomes 'embark' (I've seen this before).
'and' says to put letters next to each other.
'depart' becomes 'go' ('go' can be a synonym of 'depart').
'embark' with its last letter removed is 'embar'.
'embar'+'go'='EMBARGO'
(Other definitions for embargo that I've seen before include "Trading ban" , "restrict trade" , "Legal restraint" , "Admiralty order" , "Commercial ban" .)