Captain in "The Mysterious Island"
I believe the answer is:
'captain in the mysterious island' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for nemo that I've seen before include "Captain of the Nautilus" , "Literary captain" , "- me impune lacessit (motto of Scotland)" , "Finding -, animated film" , "Jules Verne's submarine captain" .)