Not of this world (5)
'not of this world?' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for ethereal that I've seen before include "Extremely delicate and light; otherworldly" , "Warm approval" , "Having an unreal lightness or delicateness" , "Having great lightness and delicacy" , "'Extremely delicate, almost not of this world (8)'" .)
'not of this world' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for alien that I've seen before include "Not native" , "Foreign - film directed by Ridley Scott" , "Outlandish" , "Foreign, strange" , "Little green man, perhaps" .)