noun

1. a place where plays, operas, films, etc. are presented; esp., a building or outdoor structure expressly designed for such presentations
2. any place resembling a theater, esp. a lecture hall, surgical clinic, etc., having the floor of the seating space raked
3. any place where events take place; scene of operations; specif., an area of military operations, as in a war a commander in the Southern Pacific theater
4. 1. the dramatic art or dramatic works; drama
   2. the theatrical world; people engaged in theatrical activity
   3. the legitimate theater, as distinguished from films, TV, etc.: often with the
5. theatrical technique, production, etc. with reference to its effectiveness a play that is good theater

Etymology: ME theatre < OFr < L theatrum < Gr theatron < base of theasthai, to see, view < IE base *dhāu-, to see > Gr thauma, miracle