Fine Greek character at top labour court (5)
I believe the answer is:
mulct
'fine' is the definition.
(synonyms)
'greek character at top labour court' is the wordplay.
'greek character' becomes 'mu' (letter from the Greek alphabet).
'at' says to put letters next to each other.
'top' says to take the initial letters.
'court' becomes 'ct' (abbreviation used in road names).
The first letter of 'labour' is 'l'.
'mu'+'l'+'ct'='MULCT'
(Other definitions for mulct that I've seen before include "Cheat, defraud" , "Fine - penalty" , "Extract money from (someone) by fine or taxation" , "Diddle" , "Extract money (from someone) by deceit" .)