Honest old writer (4)

I believe the answer is:

open

'honest' is the definition.
(similar in meaning)

'old writer' is the wordplay.
'old' becomes 'o' (abbreviation).
'writer' becomes 'pen' (something which writes).
'o'+'pen'='OPEN'

(Other definitions for open that I've seen before include "Frank - accessible" , "Frank - unsettled" , "with no clear favourite" , "Public" , "unresolved" .)

I've seen this clue in The Times, The Mirror and The Sun.

Want a hint initially instead of a full solution? Install my app