Left lupin out - it's copious (9)
I believe the answer is:
plentiful
'it's copious' is the definition.
(synonyms)
'left lupin out' is the wordplay.
'out' indicates anagramming the letters (out can mean wrong or inaccurate).
'left'+'lupin'='leftlupin'
'leftlupin' with letters rearranged gives 'PLENTIFUL'.
(Other definitions for plentiful that I've seen before include "Abundant - profuse" , "Existing in great quantities" , "Abundant, copious" , "Productive" , "common" .)