Southern bed for highlander (4)
I believe the answer is:
scot
'highlander' is the definition.
'southern bed' is the wordplay.
'southern' becomes 's' (abbreviation).
'bed' becomes 'cot' (cot is a kind of bed).
's'+'cot'='SCOT'
'for' acts as a link.
(Other definitions for scot that I've seen before include "Someone from north of the border?" , "Glaswegian perhaps" , "British northerner" , "Highlander, say" , "Jock?" .)