carriage
carriage, 1
1. An inclined beam which supports the steps or adds support between the strings of a wooden staircase, usually between the wall and outer string. Also called a carriage piece, horse, roughstring.
2. In theater stage equipment, a counterweight arbor.
3. A movable frame on which some other movable part or object is supported.
McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc.