Greek character in Shorter Collins? (3)
I believe the answer is:
phi
'greek character' is the definition.
(letter from the Greek alphabet)
'shorter collins?' is the wordplay.
'shorter' means to remove the last letter.
'collins?' becomes 'Phil' (musician Phil Collins).
'phil' with its final letter removed is 'PHI'.
'in' acts as a link.
(Other definitions for phi that I've seen before include "Greek letter; hip (anag.)" , "letter to Timon?" , "Greek letter; sounds like expression of outrage" , "Greek character" , "Foreign character" .)