Photograph vessels going north (4)
I believe the answer is:
snap
'photograph' is the definition.
(synonyms)
'vessels going north' is the wordplay.
'vessels' becomes 'pans' (I've seen this before).
'going north' says the letters should be written backwards.
'pans' in reverse letter order is 'SNAP'.
(Other definitions for snap that I've seen before include "Click! - a photograph!" , "you may take on holiday" , "piece of cake" , "Break like informal photo" , "Go to pieces < , it's said, quickly" .)