Cabinet enters, raising "Cheerio, Mr Attlee!" (7)
I believe the answer is:
armoire
'cabinet' is the definition.
(type of item of furniture)
'enters raising cheerio mr attlee' is the wordplay.
'raising' is a reversal indicator.
'enters' says the answer is hidden in the clue (I've seen 'entering' mean this).
'eriomra' is hidden in the letters of 'cheerio mr attlee'.
'eriomra' written backwards gives 'ARMOIRE'.
(Other definitions for armoire that I've seen before include "Cabinet originally used for storing weapons" , "Cupboard" , "Large wardrobe - more air (anag)" , "Large wardrobe or cabinet" , "item of furniture" .)