Abridged version of opera standard (4)
I believe the answer is:
norm
'standard' is the definition.
(norm is a kind of standard)
'abridged version of opera' is the wordplay.
'abridged version of' means to remove the last letter.
'opera' becomes 'norma' (I've seen this before).
'norma' with its last letter taken off is 'NORM'.
(Other definitions for norm that I've seen before include "What is conventional, regular" , "Typical pattern or situation" , "'Standard, usual (4)'" , "Bacterium, virus, etc" , "Standard regarded as typical" .)