Vicious to stuff workers as well (7)
I believe the answer is:
besides
'as well' is the definition.
(both can mean 'in addition')
'vicious to stuff workers' is the wordplay.
'vicious' becomes 'sid' (Sid Vicious).
'to stuff' indicates putting letters inside.
'workers' becomes 'bees'.
'sid' going into 'bees' is 'BESIDES'.
(Other definitions for besides that I've seen before include "In addition, as well" , "Apart from" , "What's more" , "Additionally" , "also is available" .)