Crossword Genius

Frank has a letter to write (4)

Ross

I believe the answer is:

open

'frank' is the definition.
('open' can be a synonym of 'frank')

'a letter to write' is the wordplay.
'a letter' becomes 'o'.
'to' says to put letters next to each other.
'write' becomes 'pen' ('pen' can be a synonym of 'write').
'o'+'pen'='OPEN'

'has' is the link.

(Other definitions for open that I've seen before include "Undecided" , "Candid; ajar" , "Admitting customers" , "sporting competition" , "Traditional room heater" .)

I've seen this clue in the Evening Standard.
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