theater

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

• noun A building, room, or outdoor structure for the presentation of plays, films, or other dramatic performances.
• noun A room with tiers of seats used for lectures or demonstrations.
• noun Dramatic literature or its performance; drama.
• noun The milieu of actors and playwrights.
• noun The quality or effectiveness of a theatrical production.
• noun Dramatic material or the use of such material.
• noun The audience assembled for a dramatic performance.
• noun A place that is the setting for dramatic events.
• noun A large geographic area in which military operations are coordinated.

from The Century Dictionary.

• noun A building appropriated to the representation of dramatic spectacles; a play-house.
• noun A room, hall, or other place, with a platform at one end, and ranks of seats rising stepwise as the tiers recede from the center, or otherwise so arranged that a body of spectators can have an unobstructed view of the platform.
• noun A place rising by steps or gradations like the seats of a theater.
• noun A place of action or exhibition; a field of operations; the locality or scene where a series of events takes place or may be observed; scene; seat: as, the theater of war.
• noun The drama; the mass of dramatic literature; also, theatrical representation; the stage: as, a history of the French theater.
• noun An amphitheater; hence, a circular reservoir or receptacle; a basin.

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

• noun An edifice in which dramatic performances or spectacles are exhibited for the amusement of spectators; anciently uncovered, except the stage, but in modern times roofed.
• noun Any room adapted to the exhibition of any performances before an assembly, as public lectures, scholastic exercises, anatomical demonstrations, surgical operations, etc.
• noun That which resembles a theater in form, use, or the like; a place rising by steps or gradations, like the seats of a theater.
• noun obsolete A sphere or scheme of operation.
• noun A place or region where great events are enacted.

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

• noun A place or building, consisting of a stage and seating, in which an audience gathers to watch plays, musical performances, public ceremonies, and so on.
• noun A region where a particular action takes place; a specific field of action, usually with reference to war.
• noun A lecture theatre.
• noun medicine An operating theatre or locale for human experimentation.
• noun US A cinema.
• noun Drama or performance as a profession or artform.

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

• noun a region in which active military operations are in progress
• noun the art of writing and producing plays
• noun a building where theatrical performances or motion-picture shows can be presented