Fantastic lionesses, silent (9)
I believe the answer is:
noiseless
'silent' is the definition.
(I've seen this before)
'fantastic lionesses' is the wordplay.
'fantastic' is an anagram indicator (a fantastic or improbable ordering of the letters).
'lionesses' is an anagram of 'NOISELESS'.
(Other definitions for noiseless that I've seen before include "Silent, quiet" , "with a silencer?" , "Lionesses (anag) - making no sound" , "Mum" , "unsound?" .)