Frank has nothing to write (4)
I believe the answer is:
open
'frank' is the definition.
(synonyms)
'nothing to write' is the wordplay.
'nothing' becomes 'O' (O resembles 0).
'to' says to put letters next to each other.
'write' becomes 'pen' (synonyms).
'o'+'pen'='OPEN'
'has' acts as a link.
(Other definitions for open that I've seen before include "Start - frank" , "Agape" , "Accessible - candid" , "unresolved" , "Candid - ready for business" .)