Flat hire charge includes copper gong (9)
I believe the answer is:
recumbent
'flat' is the definition.
(thesaurus)
'charge includes copper gong' is the wordplay.
'charge' becomes 'rent' (I've seen this in other clues**).
'includes' means one lot of letters goes inside another.
'copper' becomes 'cu' (chemical symbol).
'gong' becomes 'mbe' (Member of the Order of the British Empire).
'cu'+'mbe'='cumbe'
'rent' going around 'cumbe' is 'RECUMBENT'.
'hire' is the link.
This may not be correct. It may be part of another bit of the clue.
(Other definitions for recumbent that I've seen before include "Lying down comfortably" , "flat?" .)