Belittle Greek character impaled from below (8)
I believe the answer is:
derogate
'belittle' is the definition.
(synonyms)
'greek character impaled from below' is the wordplay.
'greek character' becomes 'eta' (letter from the Greek alphabet).
'impaled' becomes 'gored' (gore can mean to stab or impale).
'from below' says the letters should be written backwards (in a down clue, letters go up).
'eta'+'gored'='etagored'
'etagored' backwards is 'DEROGATE'.
(Other definitions for derogate that I've seen before include "Disparage" , "Allow a rule to be broken" .)