triforium
noun
tri·fo·ri·um trī-ˈfȯr-ē-əm 
plural triforia trī-ˈfȯr-ē-ə
: a gallery forming an upper story to the aisle of a church and typically an arcaded story between the nave arches and clerestory
Example Sentences
Recent Examples on the Web The triforium is opening up to the public on June 11 as a new museum called the Queen’s Diamond Jubilee Galleries. 
Brigit Katz, Smithsonian, 7 June 2018 High above the heads of visitors, in a gallery called the triforium, are 14 larger fan coil units that dump cool air down to sweltering summer visitors. Sharon Otterman, New York Times, 14 Mar. 2018
Brigit Katz, Smithsonian, 7 June 2018 High above the heads of visitors, in a gallery called the triforium, are 14 larger fan coil units that dump cool air down to sweltering summer visitors. Sharon Otterman, New York Times, 14 Mar. 2018 Word History
Etymology
Medieval Latin
First Known Use
1703, in the meaning defined above