Ring writer Frank (4)
I believe the answer is:
open
'frank' is the definition.
(synonyms)
'ring writer' is the wordplay.
'ring' becomes 'o' (letter resembling a ring).
'writer' becomes 'pen' (something which writes).
'o'+'pen'='OPEN'
(Other definitions for open that I've seen before include "Widely known" , "Unlock" , "Frank; unobstructed" , "Admitting customers" , "With which to offer hearty welcome" .)