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' (looks like zero - 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" .)