Writer left with yen, quickly (7)
I believe the answer is:
swiftly
'quickly' is the definition.
(I've seen this before)
'writer left with yen' is the wordplay.
'writer' becomes 'swift' (Jonathan Swift, 1667-1745).
'left' becomes 'l' (common abbreviation).
'with' means one lot of letters go next to another.
'yen' becomes 'y' (resembles the symbol for the currency of Japan).
'swift'+'l'+'y'='SWIFTLY'
(Other definitions for swiftly that I've seen before include "Quickly" , "at speed" .)