Crossword Genius

A long letter (5)

Ross

I believe the answer is:

aitch

'letter' is the definition.
(aitch is a kind of letter)

'a long' is the wordplay.
'long' becomes 'itch' (I've seen this before).
'a'+'itch'='AITCH'

(Other definitions for aitch that I've seen before include "first bit of hymn?" , "what some drop?" , "bone" , "The letter h in full" , "It's dropped by Cockneys" .)

I've seen this clue in The Telegraph and The Guardian.
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