1. A window having three sashes of the same height and in the same plane; there is a wide rectangular sash at its center and a narrower sash on each side; essentially the same as a Palladian window with the rounded head of the center sash lopped off at the top.
2. Same as treble sash.
McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc.