Letter from Greece is a small matter (4)
I believe the answer is:
iota
'letter from greece' is the definition.
(letter from the Greek alphabet)
'is a small matter' is the wordplay.
'is a small' becomes 'io' (I can't justify this - if you can you should give a lot more credence to this answer).
'matter' becomes 'Ta' (Ta is an example).
'io'+'ta'='IOTA'
Can you help me to learn more?
(Other definitions for iota that I've seen before include "Gr. letter; small amount" , "Just a jot, from Greek alphabet" , "Smidgen" , "Foreign character" , "Just a jot, like Greek letter" .)