Monstrous female, noted Liverpudlian you say? (6)
I believe the answer is:
scylla
'monstrous female' is the definition.
(sea monster in Greek myth)
'noted liverpudlian you say?' is the wordplay.
'noted liverpudlian' becomes 'Cilla' (Cilla Black was from Liverpool).
'you say?' shows a homophone (sound like).
'cilla' sounds like 'SCYLLA'.
(Other definitions for scylla that I've seen before include "Mythical rock" , "Rock, across from 21" , "danger to shipping" , "Charybdis counterpart" , "In Greek myth, sea monster who lived in cave opposite whirlpool Charybdis" .)