Greek character returning to river shows spirit (3)
I believe the answer is:
rum
'spirit' is the definition.
(I've seen this before)
'greek character returning to river' is the wordplay.
'greek character' becomes 'mu' (letter from the Greek alphabet**).
'returning' says the letters should be written backwards.
'to' is a charade indicator (letters next to each other) (I've seen this in other clues).
'river' becomes 'r'.
'mu' backwards is 'um'.
'um' after 'r' is 'RUM'.
'shows' is the link.
(Other definitions for rum that I've seen before include "Odd like drink distilled from molasses" , "An alcoholic spirit - sounds odd" , "Sugar-cane spirit" , "Droll" , "Unusual" .)