Initially when to expect a letter from Greece (3)
I believe the answer is:
eta
'letter from greece' is the definition.
(letter from the Greek alphabet)
'initially when to expect a' is the wordplay.
I cannot quite see how this works, but
'when' could be 'e' (I've seen this in other clues) and 'e' is found in the answer.
'a' is within the answer.
A single letter 't' remains which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for eta that I've seen before include "indicating when flight is due" , "Greek letter - time due (abbr)" , "Greek letter E; estimated time of arrival (abbr.)" , "giving expected termination of journey" , "when you can hope to receive it" .)