A window with three vertical sliding sashes that allow the window to open to two-thirds of its height. See also: French window
Illustrated Dictionary of Architecture Copyright © 2012, 2002, 1998 by The McGraw-Hill Companies, Inc. All rights reserved
A window having three vertically sliding sashes, each closing a different part of the window; the weight of each sash is counterbalanced for ease of opening and closing; same as treble sash.
McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc.