Rub out part of opera section (5)
I believe the answer is:
erase
'rub out' is the definition.
(I know that rub out can be written as erase)
'part of opera section' is the wordplay.
'part of' indicates the answer is hidden within the clue.
'ERASE' can be found hidden inside 'opera section'.
(Other definitions for erase that I've seen before include "Remove, wipe out" , "Blot out" , "Obliterate" , "Remove all traces of" , "Put out of mind" .)