Moan when end falls off auto (3)
I believe the answer is:
car
'auto' is the definition.
(I know that auto can be written as car)
'moan when end falls off' is the wordplay.
'moan' becomes 'carp' (carp can mean to moan or complain).
'when end falls off' means to remove the last letter.
'carp' with its last letter taken away is 'CAR'.
(Other definitions for car that I've seen before include "estate, perhaps" , "Personal vehicle" , "Automobile" , "saloon perhaps" , "Means of transport" .)