triforium
Concise Oxford English Dictionary © 2008 Oxford University Press:
triforium /trʌɪˈfɔːrɪəm/
▶noun (pl. triforia /-rɪə/) a gallery or arcade above the arches of the nave, choir, and transepts of a church.
– origin C18: from Anglo-Latin, of unknown origin.
'triforium' also found in these Oxford entries:

