Chambers of Austria dismiss America (5)
I believe the answer is:
atria
'chambers' is the definition.
(atrium is a kind of chamber)
'austria dismiss america' is the wordplay.
'austria' becomes 'a'.
'dismiss' becomes 'tri' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'america' becomes 'a' (common abbreviation - e.g. in organisation names).
'a'+'tri'+'a'='ATRIA'
'of' acts as a link.
Can you help me to learn more?
(Other definitions for atria that I've seen before include "Central courtyards" , "Open courts of Roman houses" , "Central courts, halls" , "Open-roofed courts" , "Public spaces with galleries" .)