Material without embellishment — rubbish cast outside (7)
I believe the answer is:
tabaret
'cast outside' is the definition.
The definition suggests a singular noun which matches the answer.
'material without embellishment rubbish' is the wordplay.
'material' becomes 'aba' (aba is a kind of material).
'without' indicates putting letters inside (some letters go outside or 'without' others).
'embellishment rubbish' becomes 'tret' (I can't justify this - if you can you should give a lot more credence to this answer).
'aba' put into 'tret' is 'TABARET'.
Can you help me to learn more?
(Other definitions for tabaret that I've seen before include "Beat tar out of upholsterer's silk fabric" , "material" .)