French bill -- almost everything's extra (10)
I believe the answer is:
additional
'extra' is the definition.
(extra means additional)
'french bill almost everything's' is the wordplay.
'french bill' becomes 'addition' ('bill' in French).
'almost' means to remove the last letter (most of the word but not all of it).
'everything' becomes 'all' (all things).
'all' with its last letter taken off is 'al'.
'addition'+'al'='ADDITIONAL'
(Other definitions for additional that I've seen before include "with sums, perhaps" , "Extra" .)