Cold greeting in Greek letter (3)
I believe the answer is:
chi
'greek letter' is the definition.
(letter of the Greek alphabet)
'cold greeting' is the wordplay.
'cold' becomes 'C' (eg on taps).
'greeting' becomes 'hi' (hi is a kind of greeting).
'c'+'hi'='CHI'
'in' acts as a link.
(Other definitions for chi that I've seen before include "Chinese life-force" , "T'ai -, martial art" , "Classical symbol" , "Twenty-second Greek letter" , "foreign character" .)