Mickey's companion, an alien (4)
I believe the answer is:
finn
This might be a double definition.
'mickey's companion' is the first definition.
The definition and answer can be both people as well as being singular nouns.
Perhaps there's a link between them I don't understand?
'alien' is the second definition.
The answer and definition can be both people as well as being singular nouns.
Perhaps you can see an association between them that I don't see?
'an' is the link.
Can you help me to learn more?
(Other definitions for finn that I've seen before include "EU statesman" , "adventurer in Mark Twain story" , "hero of American fiction" , "National" , "Northern European" .)