Charlie greeting a character from Athens (3)
I believe the answer is:
chi
'a character from athens' is the definition.
(letter from the Greek alphabet)
'charlie greeting' is the wordplay.
'charlie' becomes 'C' (phonetic alphabet: alpha, bravo, charlie etc.).
'greeting' becomes 'hi' (hi is a kind of greeting).
'c'+'hi'='CHI'
(Other definitions for chi that I've seen before include "seen in Greek writing" , "One character abroad" , "Twenty-second Greek letter" , "character in Thessaloniki" , "Mental projection" .)