At right angles to the length of a ship (5)
I believe the answer is:
abeam
'at right angles to the length of a ship' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for abeam that I've seen before include "To the right or left of the centre of the ship" , "At right angles to ship's length" , "The way sailor goes across ship" , "angled across the plane" , "going from one side to the other" .)