Butterfly is someone looked up to by Lieutenant Pinkerton? (7)
I believe the answer is:
admiral
I believe this clue is a double definition.
'butterfly' is the first definition.
(admiral is a kind of butterfly)
'someone looked up to by lieutenant pinkerton?' is the second definition.
(Lieutenant Pinkerton is a fictional naval officer)
'is' acts as a link.
(Other definitions for admiral that I've seen before include "Highest naval rank" , "Eg, Nelson" , "Red butterfly at sea?" , "Red butterfly in charge of the fleet" , "Brightly coloured butterfly" .)