Nothing to write, to be frank (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' means one lot of letters go next to another.
'write' becomes 'pen' (synonyms).
'o'+'pen'='OPEN'
'to be' acts as a link.
(Other definitions for open that I've seen before include "Frank - accessible" , "sporting competition" , "Frank and unlocked" , "gaping" , "Available for business, exposed" .)