n. - 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.
n. - Any room adapted to the exhibition of any performances before an assembly, as public lectures, scholastic exercises, anatomical demonstrations, surgical operations, etc.
n. - That which resembles a theater in form, use, or the like; a place rising by steps or gradations, like the seats of a theater.
n. - A sphere or scheme of operation.
n. - A place or region where great events are enacted; as, the theater of war.