1. 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.
2. Any room adapted to the exhibition of any performances before an assembly, as public lectures, scholastic exercises, anatomical demonstrations, surgical operations, etc.
3. That which resembles a theater in form, use, or the like; a place rising by steps or gradations, like the seats of a theater. Shade above shade, a woody theater Of stateliest view. (milton)
4. A sphere or scheme of operation. For if a man can be partaker of God's theater, he shall likewise be partaker of God's rest. (bacon)
5. A place or region where great events are enacted; as, the theater of war.
Origin: F. Theatre, L. Theatrum, Gr, fr. To see, view; cf. Skr. Dhya to meditate, think. Cf. Theory.