Venerated Egyptian flag, really raised on high (6)
I believe the answer is:
osiris
'venerated egyptian' is the definition.
(Osiris was an Egyptian god)
'flag really raised on high' is the wordplay.
'flag' becomes 'iris' (type of iris flower).
'really' becomes 'so' (both can mean 'extremely').
'raised' says the letters should be written backwards (going up in a down clue).
'on high' means one lot of letters go next to another (in a down clue, some letters go higher than others).
'so' backwards is 'os'.
'iris' after 'os' is 'OSIRIS'.
(Other definitions for osiris that I've seen before include "God, husband of Isis" , "Egyptian god, father of Horus" , "underworld boss" , "dead judge?" , "Husband of Isis, father of Horus - sis or I (anag)" .)