Working to create a large base for theatre event (11)
I believe the answer is:
operational
'working' is the definition.
(thesaurus)
'a large base for theatre event' is the wordplay.
'large' becomes 'l'.
'base for' is a charade indicator (letters next to each other) (some letters act as a base underneath others).
'theatre event' becomes 'operation' (event that takes place in an operating theatre).
'a'+'l'='al'
'al' after 'operation' is 'OPERATIONAL'.
'to create' acts as a link.
(Other definitions for operational that I've seen before include "In working order" , "Ready for action" , "Ready for use" , "working satisfactorily?" , "running" .)