Foreigners (6)
I believe the answer is:
aliens
'foreigners' is the definition.
('alien' can be a synonym of 'foreigner')
This is all the clue.
(Other definitions for aliens that I've seen before include "Beings from another planet" , "Foreigners or extraterrestrials" , "Non-nationals - perhaps from Mars?" , "Outsiders" , "Forms of life assumed to exist outside Earth" .)