Staunch Arab, back installing a place for sweaters (5,4)
I believe the answer is:
steam room
'place for sweaters' is the definition.
(place where people sweat)
'staunch arab back installing a' is the wordplay.
'staunch' becomes 'stem' (synonyms).
'arab' becomes 'moor' (Moor could historically mean a North African).
'back' is a reversal indicator.
'installing' indicates putting letters inside (I've seen this in other clues).
'moor' back-to-front is 'room'.
'stem'+'room'='stemroom'
'stemroom' enclosing 'a' is 'STEAM ROOM'.
(Other definitions for steam room that I've seen before include "sauna" , "Vapour bath -- more atoms (anag)" .)