Second letter after epsilon (3)
I believe the answer is:
eta
'second letter after epsilon' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for eta that I've seen before include "Foreign letter" , "Greek letter - Basque nationalist movement" , "When you'd expect to see" , "Member of Greek set a" , "giving expected termination of journey" .)