Quiet eccentric loses it lacking quality (6)
I believe the answer is:
shoddy
'it lacking quality' is the definition.
The definition suggests a singular noun which matches the answer. I also know that 'quality' relates to this answer.
'quiet eccentric loses' is the wordplay.
'quiet' becomes 'sh' (both can be said to tell someone to be quiet).
'eccentric' becomes 'odd' (odd can mean eccentric or unusual).
'loses' becomes 'y' (I am not sure about this - if you are sure you should believe this answer much more).
'sh'+'odd'+'y'='SHODDY'
Can you help me to learn more?
(Other definitions for shoddy that I've seen before include "inferior cloth" , "Cheap and tawdry" , "Of poor quality or workmanship" , "Badly made or done" , "clippings in this" .)