1) a theatre, a place in which games and dramatic spectacles are exhibited, and public assemblies held (for the Greeks used the theatre also as a forum)
2) a public show
2a) metaphorically, a man who is exhibited to be gazed at and made sport of
Part of Speech: noun neuter
Citing in TDNT: 3:42, 318
From G2300; a place for public show ("theatre"), that is, general audience room; by implication a show itself (figuratively): - spectacle, theatre.
These two sites give similar information, with the definition from several dictionaries and statistics on the use of the word.
Perseus Digital Library
University of Chicago's Logion lexicon
Thayer's dictionary plus other information.
From this site's dictionary (in Italian)
Click on the first column to search for that word as a form of the root θέατρον; click on the second column to search for that grammatical form of the root θέατρον; click on the third column to search for that word and grammatical form; click on the total to search for the root θέατρον.