Major production
(Other definitions for opus that I've seen before include "Work (of a composer?)" , "Composition - magnum __" , "Composer's catalogue number" , "(Numbered) musical composition" , "Musical composition in the soup" .)
'major production' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for ado that I've seen before include "Song and dance" , "'Much ... About Nothing, Shakespeare play (3)'" , "Nothing caused much around 1598" , "Busy activity, trouble" , "Fuss, difficulty" .)