Caledonians needing a bunk in the ship (5)
I believe the answer is:
scots
'caledonians' is the definition.
(I've seen this in another clue)
'a bunk in the ship' is the wordplay.
'a bunk' becomes 'cot' (I've seen this in another clue).
'in the' means one lot of letters goes inside another.
'ship' becomes 'SS' (prefix in ship names eg SS Great Britain).
'cot' inserted inside 'ss' is 'SCOTS'.
'needing' is the link.
(Other definitions for scots that I've seen before include "A UK language" , "Northern language" , "Glaswegians, Aberdonians etc" , "Folk from Fife" , "- Greys, - pine" .)