I turned to a letter from Greece (4)
I believe the answer is:
iota
'letter from greece' is the definition.
(letter from the Greek alphabet)
'i turned to a' is the wordplay.
'turned' says the letters should be written in reverse.
'to' written backwards gives 'ot'.
'i'+'ot'+'a'='IOTA'
(Other definitions for iota that I've seen before include "Grain" , "The smallest possible amount, or the Greek i" , "letter from Greece" , "Smidgen" , "Ninth Greek character" .)