This planetary inhabitant left in hearing aid? (9)
I believe the answer is:
earthling
'this planetary inhabitant' is the definition.
'earthling' can be an answer for 'inhabitant' (earthling is a kind of inhabitant). I am not sure about the 'this planetary' bit.
'left in hearing aid?' is the wordplay.
'left' becomes 'l' (common abbreviation).
'in' is an insertion indicator.
'hearing' becomes 'ear' (ear is a kind of hearing).
'aid?' becomes 'thing' (I can't explain this - if you can you should believe this answer much more).
'ear'+'thing'='earthing'
'l' inserted into 'earthing' is 'EARTHLING'.
Can you help me to learn more?
(Other definitions for earthling that I've seen before include "Man of the world" , "Human being (sci-fi)" , "man so to be called from space?" , "sci-fi character" .)