Pair maybe 200 metres beyond Belgium's capital (5)
I believe the answer is:
brace
'pair' is the definition.
(synonyms)
'200 metres beyond belgium's capital' is the wordplay.
'200 metres' becomes 'race' (the 200 metres is a race).
'beyond' is a charade indicator (letters next to each other).
'capital' says to take the initial letters.
The initial letter of 'belgium' is 'b'.
'race' put after 'b' is 'BRACE'.
'maybe' is the link.
(Other definitions for brace that I've seen before include "Tighten, strengthen" , "Support - pair" , "Pair of game-birds" , "Support or hold steady" , "Stanchion" .)