Alfresco opera in translation (4-3)
I believe the answer is:
'alfresco' is the definition.
(I know that alfresco can be written as open-air)
'opera in translation' is the wordplay.
'translation' is an anagram indicator.
'operain' with letters rearranged gives 'OPEN-AIR'.
(Other definitions for open-air that I've seen before include "not below roof" , "outside" , "Exposed to the elements" , "Alfresco" , "Taking place outdoors" .)