Object? Fine and good (5)
I believe the answer is:
thing
'object?' is the definition.
(thing is a kind of object)
'fine and good' is the wordplay.
'fine' becomes 'thin' ('thin' can be similar in meaning to 'fine').
'and' says to put letters next to each other.
'good' becomes 'g' (abbreviation).
'thin'+'g'='THING'
(Other definitions for thing that I've seen before include "A creature" , "Affair - matter" , "Object; gadget" , "An unnamed object or item" , "Object, artefact" .)