Five hundred wrongly laid off -- it's a bloomer (8)
I believe the answer is:
daffodil
'a bloomer' is the definition.
(I've seen this before)
'five hundred wrongly laid off' is the wordplay.
'five hundred' becomes 'd' ('D' can be a synonym of 'five hundred').
'wrongly' is an anagram indicator (I've seen this in other clues).
'laid'+'off'='laidoff'
'laidoff' anagrammed gives 'affodil'.
'd'+'affodil'='DAFFODIL'
'it's' acts as a link.
(Other definitions for daffodil that I've seen before include "Flower, emblem of Wales" , "Yellow spring flower beloved of Wordsworth" , "Popular yellow flower of spring - ask Wordsworth" , "Bloomer" , "Something yellow for spring" .)