Ready briefcase to impress English king (6)
I believe the answer is:
shekel
'ready briefcase' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'to impress english king' is the wordplay.
'to' becomes 'shel' (I can't explain this - if you can you should believe this answer much more).
'impress' means one lot of letters goes inside another (impress can mean enlist or recruit).
'english' becomes 'e' (abbreviation).
'king' becomes 'k'.
'e'+'k'='ek'
'shel' placed around 'ek' is 'SHEKEL'.
Can you help me to learn more?
(Other definitions for shekel that I've seen before include "Israeli monetary unit" , "Basic unit of money in Israel" , "Small price" , "Israeli currency unit" , "Middle East money" .)