At the front of the building strong wine could be served before Irish Chamber Orchestra appears (7)
I believe the answer is:
portico
'at' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for portico that I've seen before include "gallery, perhaps" , "Covered walkway" , "Grand entrance" , "Colonnade, covered porch" , "small architectural feature" .)