Fine head on glorious object (5)
I believe the answer is:
thing
'object' is the definition.
(an object is a thing or item)
'fine head on glorious' is the wordplay.
'fine' becomes 'thin' (similar in meaning).
'head on' suggests taking the first letters.
The initial letter of 'glorious' is 'g'.
'thin'+'g'='THING'
(Other definitions for thing that I've seen before include "Individual object" , "Unspecified object" , "See 1" , "An unnamed object or item" , "cup of tea" .)