Lost out a great deal (4)
I believe the answer is:
lots
'a great deal' is the definition.
(I've seen this in another clue)
'lost out' is the wordplay.
'out' indicates an anagram (out can mean wrong or inaccurate).
'lost' with letters rearranged gives 'LOTS'.
(Other definitions for lots that I've seen before include "Large numbers at auction" , "Great quantities" , "a crowd?" , "Something to draw" , "Oodles" .)