Henry beset by metallic sound: object (5)
I believe the answer is:
thing
'object' is the definition.
(thing is a kind of object)
'henry beset by metallic sound' is the wordplay.
'henry' becomes 'h' ('H' can be a synonym of 'henry').
'beset by' means one lot of letters goes inside another ('beset' could historically mean 'cover').
'metallic sound' becomes 'ting'.
'h' going into 'ting' is 'THING'.
(Other definitions for thing that I've seen before include "Night (anag)" , "Obsession" , "Affair - matter" , "Individual unit" , "Unspecified object" .)