Letter before psi (3)
I believe the answer is:
chi
'letter before psi' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for chi that I've seen before include "foreign character" , "Greek letter; Chinese life force" , "One character abroad" , "Twenty-second Greek letter" , "The life force, according to traditional Chinese medicine" .)