lagging

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Insulation used to prevent heat diffusion, as from a steam pipe.
• noun A wooden frame built especially to support the sides of an arch until the keystone is positioned.

from The Century Dictionary.

• noun The act of walking or moving slowly, or of falling behind.
• noun In architecture, the planking, consisting of narrow strips, extending from one rib of the centering of an arch, vault, or tunnel to another, and affording direct support to the voussoirs until the arch or vault is closed in.
• noun In mining, strips of wood or light timbers laid across the stulls in the drifts to prevent fragments of rock from falling through.
• noun In machinery, same as deading.
• noun A covering for the face of a pulley, designed to increase its effective diameter or to augment the adhesion of the belt.
• noun Same as lag, n., 7.
• noun Nautical, the part of a barrel-stave beyond the head. Also spelled laggin.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Mach.) The clothing (esp., an outer, wooden covering), as of a steam cylinder, applied to prevent the radiation of heat; a covering of lags; -- called also deading and cleading.
• noun Lags, collectively; narrow planks extending from one rib to another in the centering of arches.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adjective falling behind, not keeping up the pace
• adjective Occurring after; indicating the later phase of
• noun The covering of something with strips of felt, wood etc, either as insulation or for protection
• noun The material so used
• verb Present participle of lag.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun used to wrap around pipes or boilers or laid in attics to prevent loss of heat