Dictionary.net

A structure, usually in the form of a tower, containing signal-lights for the guidance of vessels at night, at dangerous points of a coast, shoals, etc. They are usually erected by government, and subject to governmental regulation.

n. A tower 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— distinguishable from the number. or position, or colour of the lights, or from the periods of time in which a revolving light becomes visible or obscured.