Prompt writer (5)
I believe the answer is:
swift
I believe this clue is a double definition.
'prompt' is the first definition.
(I've seen this before)
'writer' is the second definition.
(Jonathan Swift, 1667-1745)
(Other definitions for swift that I've seen before include "Expeditious" , "Fast-moving bird" , "Fast moving; bird" , "Racy" , "wit?" .)