Exposed, a king in retreat heading west (5)
I believe the answer is:
naked
'exposed' is the definition.
(thesaurus)
'a king in retreat heading west' is the wordplay.
'king' becomes 'k'.
'in' means one lot of letters goes inside another.
'retreat' becomes 'den'.
'heading west' says the letters should be written in reverse.
'den' reversed gives 'ned'.
'a'+'k'='ak'
'ak' going within 'ned' is 'NAKED'.
(Other definitions for naked that I've seen before include "In the altogether" , "Bare" , "Without clothes" , "Blatant" , "In one's birthday suit" .)