A letter from Greece (4)

I believe the answer is:

beta

I'm a little stuck... Click here to teach me more about this clue!

'a letter from greece' is the definition.
(letter from the Greek alphabet)

'letter from greece' is the wordplay.
'letter' becomes 'b'.
'from greece' becomes 'eta' (I can't explain this - if you can you should give a lot more credence to this answer).
'b'+'eta'='BETA'

Can you help me to learn more?

(Other definitions for beta that I've seen before include "Second Greek letter - beat that" , "Old character" , "Letter before gamma" , "Second highest grade of mark" , "Greek letter -- second in order of importance" .)

I've seen this clue in the Evening Standard.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.