I look up article on the comic opera (8)
I believe the answer is:
iolanthe
'comic opera' is the definition.
(Gilbert and Sullivan opera)
'i look up article on the' is the wordplay.
'look' becomes 'lo' (archaic exclamation meaning 'look!').
'up' is a reversal indicator (in down clue: letters go upwards).
'article' becomes 'an' (English indefinite article).
'on' means one lot of letters go next to another.
'lo' back-to-front is 'ol'.
'i'+'ol'+'an'+'the'='IOLANTHE'
(Other definitions for iolanthe that I've seen before include "G&S piece" , "G&S's eponymous fairy" , "G&S operetta" , "G&S twenty three down" , "Gilbert and Sullivan opera" .)