Man nearly detained in Kuwait on vacation (6)
I believe the answer is:
knight
'man' is the definition.
(man can mean a piece in chess)
'nearly detained in kuwait on vacation' is the wordplay.
'nearly' becomes 'nigh' (synonyms).
'detained in' is an insertion indicator.
'on vacation' means to remove the middle letters (after the inside letters have vacated the word).
'kuwait' with its middle removed is 'kt'.
'nigh' placed within 'kt' is 'KNIGHT'.
(Other definitions for knight that I've seen before include "Chesspiece which moves in the shape of an L" , "Chess piece or non-hereditary English peer" , "Mounted warrior of feudal times" , "Old horseman (on board?)" , "Horse's head on board" .)