Highlander first to sit on bed (4)
I believe the answer is:
scot
'highlander' is the definition.
(I've seen this in another clue)
'first to sit on bed' is the wordplay.
'first to' says to take the initial letters.
'on' means one lot of letters go next to another.
'bed' becomes 'cot' (cot is a kind of bed).
The first letter of 'sit' is 's'.
's'+'cot'='SCOT'
(Other definitions for scot that I've seen before include "Eg, Glasgow native" , "Native of country of the UK" , "Glaswegian perhaps" , "Payment" , "---- free: originally free from penalties of taxation" .)