Piece of furniture you reportedly can set up (4)
I believe the answer is:
unit
'piece of furniture' is the definition.
(unit of furniture)
'you reportedly can set up' is the wordplay.
'reportedly' indicates a 'sounds like' (homophone) clue.
'can' becomes 'tin' (synonyms).
'set up' says the letters should be written backwards (in a down clue, letters go up).
'you' is a homophone of 'u'.
'tin' back-to-front is 'nit'.
'u'+'nit'='UNIT'
(Other definitions for unit that I've seen before include "A considerable number of soldiers" , "Operational team" , "Item combining separate parts" , "Module" , "Constituent" .)