Flat in Cleveland (5)
I believe the answer is:
level
'flat' is the definition.
(synonyms)
'in cleveland' is the wordplay.
'in' indicates a hidden word.
'LEVEL' can be found hidden inside 'cleveland'.
(Other definitions for level that I've seen before include "Floor; surveying device" , "Not in front or behind" , "Uniform" , "Experience an evening out" , "Steady, flat, floor" .)