Document left by engineers (6)
I believe the answer is:
report
'document' is the definition.
(I've seen this before)
'left by engineers' is the wordplay.
'left' becomes 'port' (left side of a ship - opposite of starboard).
'by' is a charade indicator (letters next to each other).
'engineers' becomes 're' (Royal Engineers).
'port' after 're' is 'REPORT'.
(Other definitions for report that I've seen before include "Journalist's account - explosive noise" , "result of firing?" , "Formal account of a matter" , "Declaration" , "Narrative given by porter" .)