sheathing

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

• noun A layer of boards or of other wood or fiber materials applied to the outer studs, joists, and rafters of a building to strengthen the structure and serve as a base for an exterior weatherproof cladding.
• noun Nautical An exterior covering on the underwater part of a ship's hull that protects it against marine growths.
• noun The act of providing sheathing.

from The Century Dictionary.

• noun The act of one who sheathes.
• noun That which sheathes, covers, or protects, or may be used for such purpose.
• noun A protection for the main deck of a whaling-vessel, as pine boards, about one inch in thickness, laid over the deck to prevent it from being cut up by the spades, being burned while trying out oil, etc.
• Inclosing by or as by a sheath: as, the sheathing base of a leaf; sheathing stipules, etc. See cut under sheath, 2.

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

• Inclosing with a sheath.
• noun The casing or covering of a ship's bottom and sides; the materials for such covering.
• noun (Arch.) The first covering of boards on the outside wall of a frame house or on a timber roof; also, the material used for covering; ceiling boards in general.

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

• noun Something that wraps around or surrounds something, as a sheath encases its blade.
• verb Present participle of sheathe.

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

• noun protective covering consisting, for example, of a layer of boards applied to the studs and joists of a building to strengthen it and serve as a foundation for a weatherproof exterior