Strange, alien (7)
I believe the answer is:
unknown
I believe this clue is a double definition.
'strange' is the first definition.
(I know that strange can be written as unknown)
'alien' is the second definition.
(I know that alien can be written as unknown)
(Other definitions for unknown that I've seen before include "Strange - obscure" , "Mysterious" , "Unidentified - not explored" , "anon?" , "Not recognised by anyone" .)