billboard

from The Century Dictionary.

• noun Nautical, a projection sheathed with iron placed abaft the cathead, for the bill of the anchor to rest on. See anchor-lining.
• noun A board or tablet on which advertising bills or placards may be posted.
• noun A ticket of admission to a theatrical performance, circus, or the like, given to shopkeepers, etc., in return for billboard privileges accorded.

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

• noun (Naut.) A piece of thick plank, armed with iron plates, and fixed on the bow or fore channels of a vessel, for the bill or fluke of the anchor to rest on.
• noun A flat surface, as of a panel or of a fence, on which bills are posted; a bulletin board.

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

• noun A very large advertisement along the side of a highway.
• noun dated A flat surface, such as a panel or fence, on which bills are posted; a bulletin board.
• noun nautical A piece of thick plank, armed with iron plates, and fixed on the bow or fore channels of a vessel, for the bill or fluke of the anchor to rest on.
• noun computer graphics A sprite that always faces the screen, no matter which direction it's looked at from.

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

• noun large outdoor signboard