Floor working party to hold aggregate up (6)
I believe the answer is:
bemuse
'floor' is the definition.
(I've seen this before)
'working party to hold aggregate up' is the wordplay.
'working party' becomes 'bee' (social event for work, as in a sewing bee).
'to hold' is an insertion indicator.
'aggregate' becomes 'sum' (synonyms).
'up' says the letters should be written in reverse (in down clue: letters go upwards).
'sum' backwards is 'mus'.
'bee' placed around 'mus' is 'BEMUSE'.
(Other definitions for bemuse that I've seen before include "Floor" , "Puzzle and confuse" , "Stupefy, puzzle" , "Fox" , "Bewilder or baffle" .)