Almost the entire spoilt baker's dozen (8)
I believe the answer is:
thirteen
'baker's dozen' is the definition.
(synonyms)
'almost the entire spoilt' is the wordplay.
'almost' means to remove the last letter (almost the whole word is kept).
'spoilt' is an anagram indicator.
'the' with its last letter taken away is 'th'.
'entire' with letters rearranged gives 'irteen'.
'th'+'irteen'='THIRTEEN'
(Other definitions for thirteen that I've seen before include "this could be unlucky" , "Where situation is" , "hole possibly" , "ill-omened figure" , "Number considered unlucky" .)