Bill's on the French board (5)
I believe the answer is:
table
'board' is the definition.
(synonyms)
'bill's on the french' is the wordplay.
'bill' becomes 'tab' (tab is a kind of bill).
'on' means one lot of letters go next to another.
'the french' becomes 'le' ('the' in French).
'tab'+'le'='TABLE'
(Other definitions for table that I've seen before include "Put forward for formal discussion" , "Bleat (anag.)" , "Horizontal furniture" , "League --; multiplication --" , "Flat surfaced piece of furniture" .)