Open venue, or not, as may be (5)
I believe the answer is:
troon
'open venue' is the definition.
(golf course which has hosted the British Open)
'or not as may be' is the wordplay.
'as may be' indicates an anagram.
'or'+'not'='ornot'
'ornot' anagrammed gives 'TROON'.
(Other definitions for troon that I've seen before include "Coastal town of West Scotland" , "Open home" , "Scottish golf town" , "West Scottish town with links" , "Ayrshire golf course" .)