Perhaps Norma had some food - a common function (7)
I believe the answer is:
operate
'a common function' is the definition.
'operate' can be an answer for 'function' (I've seen this in another clue). I am not sure about the 'a common' bit.
'perhaps norma had some food' is the wordplay.
'perhaps norma' becomes 'opera' (Norma is an opera by Vincenzo Bellini).
'had some food' becomes 'te' (I can't justify this - if you can you should believe this answer much more).
'opera'+'te'='OPERATE'
Can you help me to learn more?
(Other definitions for operate that I've seen before include "Perform surgery or run a machine" , "Work - perform surgery" , "(Of machine) function" , "Perform as surgeon does" , "Manage, run" .)