viewer

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

• noun One that views, especially an onlooker or spectator.
• noun Any of various optical devices used to facilitate the viewing of photographic transparencies by illuminating or magnifying them.
• noun A person who watches television or movies.

from The Century Dictionary.

• noun One who views, surveys, or examines.
• noun Specifically— An official appointed to inspect or superintend something; an overseer; in coal-mining, the general manager, both above and below ground, of a coal-mine. This word, not at all in use in the United States, is almost obsolete in England, having become replaced by the terms mining-engineer and agent. The terms used in the United States are manager and superintendent.
• noun One of a body of jurors who are appointed by a court to view or inspect the property in controversy or the place where a crime has been committed. In Scotland two persons called showers point out the subjects to be viewed.

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

• noun One who views or examines.
• noun (Law) A person appointed to inspect highways, fences, or the like, and to report upon the same.
• noun engraving The superintendent of a coal mine.

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

• noun Someone that views some spectacle; an onlooker or spectator
• noun Someone who watches television
• noun Any optical device used to view photographic slides
• noun computing A program that displays the contents of a file of digital images; an image viewer or file viewer

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

• noun an optical device for viewing photographic transparencies
• noun a close observer; someone who looks at something (such as an exhibition of some kind)