Determination makes old king object (4)
I believe the answer is:
grit
'determination' is the definition.
(thesaurus)
'old king object' is the wordplay.
'old king' becomes 'gr' (Georgius Rex, Latin for King George).
'object' becomes 'it' (pronoun for an inanimate object).
'gr'+'it'='GRIT'
'makes' acts as a link.
(Other definitions for grit that I've seen before include "Indomitability" , "Coarse sandstone - strength of character" , "Courage, small stones" , "Small hard particles - courage" , "Determination - small stones" .)