Radiance observed over Hungary (5)
I believe the answer is:
sheen
'radiance' is the definition.
(I've seen this before)
'observed over hungary' is the wordplay.
'observed' becomes 'seen' ('seen' can be a synonym of 'observed').
'over' is an insertion indicator.
'hungary' becomes 'h'.
'seen' placed around 'h' is 'SHEEN'.
(Other definitions for sheen that I've seen before include "to the west of Putney" , "Superficial brightness" , "Acting family" , "Surface shine" , "Glow" .)