Theater (noun)

1. A building or outdoor area in which plays and other dramatic performances are given.
2. A room or hall equipped for the showing of films.
3. The branch of the performing arts concerned with the writing, production, and presentation of plays.
4. A place where a particular activity or service is based, especially one providing entertainment or instruction.
5. A place where military operations are conducted.

Origin:

Late 16th century: from french théâtre, or via latin from greek theatron "a place for viewing", from theasthai "to view".

Examples:

1. I'm going to the theater to see a play.
2. The theater was packed with people.
3. I study theater in college.
4. The military uses this building as a command and control theater.
5. The new multiplex theater has opened in the city.