Greatness alternatively in hatred (8)
I believe the answer is:
enormity
'greatness' is the definition.
(thesaurus)
'alternatively in hatred' is the wordplay.
'alternatively' becomes 'or'.
'in' means one lot of letters goes inside another.
'hatred' becomes 'enmity' (enmity is a kind of hatred).
'or' placed inside 'enmity' is 'ENORMITY'.
(Other definitions for enormity that I've seen before include "Great wickedness - more tiny (anag)" , "Evil" , "Grave crime or sin" , "Great wickedness or huge size" , "Shocking act" .)