Item of furniture ultimately not up to the task (5)
I believe the answer is:
table
'item of furniture' is the definition.
(table is a type of furniture item)
'ultimately not up to the task' is the wordplay.
'ultimately' indicates one should take the final letters.
'up to the task' becomes 'able' (I've seen this in another clue).
The final letter of 'not' is 't'.
't'+'able'='TABLE'
(Other definitions for table that I've seen before include "Board off which dinner's eaten" , "Bleat (anag.)" , "Board < put on" , "Submit for consideration" , "Article of furniture - list of facts and figures" .)