Article cheers Greek character (5)

I believe the answer is:

theta

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

'article cheers' is the wordplay.
'article' becomes 'the' (the definite article in English).
'cheers' becomes 'ta' (both can informally mean thank you).
'the'+'ta'='THETA'

(Other definitions for theta that I've seen before include "Letter to the Corinthians" , "Letter from Greece" , "letter to Greeks" , "Foreign character" , "Greek letter equivalent to th" .)

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

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