Best man's charge (4)
I believe the answer is:
ring
'best man's charge' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for ring that I've seen before include "Frodo's burden (Tolkien)" , "Arena; jewellery item" , "Circular object - sound" , "Circle that's square for boxers" , "Wedding band" .)