lighthouse

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A tall structure topped by a powerful light used as a beacon or signal to aid marine navigation.

Century Dictionary and Cyclopedia

1. n. A tower or other structure exhibiting a light or lights, for the purpose of indicating the presence of rocks, shoals, or other dangers to navigation, or for the guidance of mariners when approaching or sailing along a coast, entering a harbor, or navigating a river or other body of water. Lighthouses were formerly illuminated simply by means of a wood- or coal-fire, and afterward by candles and lamps. Coal-fires continued in general use till after the middle of the eighteenth century, and in some places many years later. The lamps in the lanterns of lighthouses in the United States are, for the most part, mechanical oil-lamps fitted with Argand burners, and employed with simple reflectors or with some form of the Fresnel lantern. Electric lighting has been tried in some lighthouses, but found objectionable on account of the depth of shadow produced by it in their immediate vicinity. In order that lighthouses may be distinguished by night, their lights vary in power, color, number, position, etc. As regards power, they are classified as of the first, second, third, or fourth order: the first two being employed in coast-lighthouses, and the others as sound-, harbor-, or river-lights. They may be fixed, revolving, flashing, or intermittent, in either single or combined colors: thus, a light may show two white flashes and a red flash followed by an interval of darkness, or the red and white flashes may alternate. These changes are obtained by various contrivances for causing the lenses, reflectors, or screens to travel in a circular path around the lamp, or to pass before it. Some lighthouses are painted with bands of color, or bear some other distinguishing mark, that their identity may be easily established in the daytime.

Wiktionary

1. n. A building, usually a tower, containing a light to warn or guide ships.

GNU Webster's 1913

1. n. A tower or other building with a powerful light at top, erected at the entrance of a port, or at some important point on a coast, to serve as a guide to mariners at night; a pharos.

WordNet 3.0

1. n. a tower with a light that gives warning of shoals to passing ships