n. 1. a. A covering used to provide thermal insulation, as from a steam pipe. b. A similar covering used to provide acoustical insulation, as on an air duct. 2. a. A plank or set of planks forming the outer surface of a centering for the construction of an arch. b. Any of various structural members or materials used as a protective sheathing, as on the ceiling of a mine tunnel or around a boiler. [From LAG2.] |
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2022 by HarperCollins Publishers. All rights reserved.