Cold greeting in foreign letter (3)
I believe the answer is:
chi
'foreign letter' is the definition.
(Greek letter)
'cold greeting' is the wordplay.
'cold' becomes 'c' (eg on taps).
'greeting' becomes 'hi' (hi is a kind of greeting).
'c'+'hi'='CHI'
'in' is the link.
(Other definitions for chi that I've seen before include "The life force, according to traditional Chinese medicine" , "Classical symbol" , "Greek letter; force in Chinese philosophy" , "character in Thessaloniki" , "foreign character" .)