Former place for an exhibition (10)
I believe the answer is:
exposition
'for an exhibition' is the definition.
('exposition' can be a synonym of 'exhibition')
'former place' is the wordplay.
'former' becomes 'ex' (prefix meaning former or onetime).
'place' becomes 'position' (positioning is a kind of placing).
'ex'+'position'='EXPOSITION'
(Other definitions for exposition that I've seen before include "large show" , "Public display" , "commentary" , "Account" , "fair" .)