Usher came out before last Arabic sovereign (4-6)

'last arabic sovereign' is the definition.
I know nothing about this answer so I can't judge whether it can be defined by this definition.

'usher came out before' is the wordplay.
'usher' becomes 'bearer' (I can't justify this - if you can you should believe this answer much more).
'out' indicates anagramming the letters (out can mean wrong or inaccurate).
'before' says to put letters next to each other.
'came' anagrammed gives 'mace'.
'bearer' put after 'mace' is 'MACE-BEARER'.

Can you help me to learn more?