American directors on ship (6)
I believe the answer is:
aboard
'on ship' is the definition.
(aboard a ship)
'american directors' is the wordplay.
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'directors' becomes 'board' (board of directors).
'a'+'board'='ABOARD'
(Other definitions for aboard that I've seen before include "Alongside" , "On a ship, train, plane or other vehicle" , "Part of the group" , "On (eg, a ship)" , "on deck" .)