In the study, additional decoration much worn (10)
I believe the answer is:
threadbare
'worn' is the definition.
(similar in meaning)
'in the study additional decoration much' is the wordplay.
'in' means one lot of letters goes inside another.
'study' becomes 'read' (synonyms).
'additional decoration much' becomes 'bar' (I can't justify this - if you can you should believe this answer much more).
'read'+'bar'='readbar'
'the' placed around 'readbar' is 'THREADBARE'.
Can you help me to learn more?
(Other definitions for threadbare that I've seen before include "Frayed" , "Tired" , "cliche-ridden" , "Thin, tattered, worn out" , "deprived of nap" .)