Losing unfurled umbrella, Simon Russell Beale unusually quiet (9)
I believe the answer is:
noiseless
'quiet' is the definition.
(similar in meaning)
'losing unfurled umbrella simon russell beale unusually' is the wordplay.
'losing unfurled' suggests deleting specific letters.
'unusually' indicates anagramming the letters.
'simon'+'russell'+'beale'='simonrussellbeale'
'simonrussellbeale' with 'umbrella' removed is 'sionssele'.
'sionssele' with letters rearranged gives 'NOISELESS'.
(Other definitions for noiseless that I've seen before include "with a silencer?" , "Silent, quiet" , "unsound?" , "Lionesses (anag) - making no sound" , "Mum" .)