Ten cheers for Greek character (4)
I believe the answer is:
iota
'greek character' is the definition.
(letter from the Greek alphabet)
'ten cheers' is the wordplay.
'ten' becomes 'io'.
'cheers' becomes 'ta' (I've seen this in other clues).
'io'+'ta'='IOTA'
'for' is the link.
(Other definitions for iota that I've seen before include "Ninth Greek character" , "Greek equivalent of the letter I" , "letter from Greece" , "Smidgeon" , "Jot, particle" .)