Four nations of Britain, with king in charge (4)
I believe the answer is:
bric
'four nations of britain with king in charge' is the definition.
I can't judge whether this definition defines the answer.
'britain with king in charge' is the wordplay.
'britain' becomes 'B' (common abbreviation as in GB).
'with' says to put letters next to each other.
'king' becomes 'R' (abbreviation for rex, king in Latin).
'in charge' becomes 'ic' (abbreviation for 'in charge').
'b'+'r'+'ic'='BRIC'
Can you help me to learn more?
(Another definition for bric that I've seen is " Knick-knacks".)