Crossword Genius

Greek character is missing from this Greek letter (5)

Ross

I believe the answer is:

theta

'greek character' is the definition.
(letter from the Greek alphabet)

'is missing from this greek letter' is the wordplay.
'missing from' is a deletion indicator.
'greek letter' becomes 'eta' (letter from the Greek alphabet).
'this' with 'is' taken out is 'th'.
'th'+'eta'='THETA'

(Other definitions for theta that I've seen before include "Character from overseas" , "classic character?" , "Letter before iota" , "Letter from Greece" , "Eighth letter of Greek alphabet" .)

I've seen this clue in The Telegraph.
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