Bearing taken by a ship on a loch (4)
I believe the answer is:
ness
'a loch' is the definition.
(Loch Ness in Scotland)
'bearing taken by a ship on' is the wordplay.
'bearing' becomes 'ne' ().
'taken' says to put letters next to each other.
'by' says to put letters next to each other.
'a ship' becomes 'SS' (prefix in ship names eg SS Great Britain).
'on' means one lot of letters go next to another.
'ne'+'ss'='NESS'
(Other definitions for ness that I've seen before include "head" , "Eliot -, led effort against Al Capone; Scots loch" , "Where you're reputed to see monster" , "Scottish Loch with legendary monster" , "Scottish Lough containing legendary monster" .)