Courage - King George had it
I believe the answer is:
grit
'courage' is the definition.
(I've seen this before)
'king george had it' is the wordplay.
'king george' becomes 'gr' (Georgius Rex).
'had' means one lot of letters go next to another.
'gr'+'it'='GRIT'
(Other definitions for grit that I've seen before include "Fragments to sprinkle on roads" , "Kind of courage or dirt" , "Determination -- coarse sandstone" , "Gumption or small pieces of stone" , "Bottle" .)