Room, average, used by 50 of us (7)
I believe the answer is:
parlour
'room' is the definition.
(parlour is a kind of room)
'average used by 50 of us' is the wordplay.
'average' becomes 'par' (average score in golf).
'used by' says to put letters next to each other.
'50' becomes 'l' (Roman numeral).
'of us' becomes 'our' (our means belonging to us).
'par'+'l'+'our'='PARLOUR'
(Other definitions for parlour that I've seen before include "Lounge, reception room" , "Living room - where farmers milk cows?" , "Beauty room?" , "Room for receiving guests in a monastery" , "Shop etc, formerly front room" .)