Greek character getting in the way of soot (4)
I believe the answer is:
smut
'soot' is the definition.
(thesaurus)
'greek character getting in the way' is the wordplay.
'greek character' becomes 'mu' (letter from the Greek alphabet**).
'getting in' means one lot of letters goes inside another.
'the way' becomes 'st'.
'mu' put within 'st' is 'SMUT'.
'of' acts as a link.
(Other definitions for smut that I've seen before include "Disease of cereal grass" , "Obscene stuff" , "Small bit of soot" , "Dirt or obscenity" , "Sooty matter" .)