Letter from abroad from Charlie with greeting (3)
I believe the answer is:
chi
'letter from abroad' is the definition.
(letter of the Greek alphabet)
'charlie with greeting' is the wordplay.
'charlie' becomes 'c' (phonetic alphabet: alpha, bravo, charlie etc.).
'with' means one lot of letters go next to another.
'greeting' becomes 'hi' (hi is a kind of greeting).
'c'+'hi'='CHI'
'from' acts as a link.
(Other definitions for chi that I've seen before include "The life force, according to traditional Chinese medicine" , "Greek character" , "Greek letter; Chinese life force" , "The 22nd letter of Greek alphabet" , "seen in Greek writing" .)