Alien’s out of hearing (6)
I believe the answer is:
exotic
'alien's' is the definition.
(synonyms)
'out of hearing' is the wordplay.
'out of' becomes 'ex'.
'hearing' becomes 'otic' (I am not sure about this - if you are sure you should believe this answer much more).
'ex'+'otic'='EXOTIC'
Can you help me to learn more?
(Other definitions for exotic that I've seen before include "Alluringly foreign" , "Weird; alien" , "Unusual and interesting" , "Unusual and showy" , "Interestingly different or strange" .)