Hearing things (4)
I believe the answer is:
ears
'hearing things' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for ears that I've seen before include "'''Friends, Romans, countrymen, lend me your ...'' (Julius Caesar) (4)'" , "''He who has ... to hear, let him hear'' (bible)" , "Locations for buds or studs?" , "Sear (anag.)" , "Listening organs" .)