A timber found on a ship (6)
I believe the answer is:
aboard
'on a ship' is the definition.
(I've seen this before)
'a timber' is the wordplay.
'timber' becomes 'board' (board is a kind of timber).
'a'+'board'='ABOARD'
'found' acts as a link.
(Other definitions for aboard that I've seen before include "On (a ship, train, etc)" , "On (eg, a ship)" , "Part of the group" , "Joined for mutual benefit" , "Alongside" .)