A place made for showing a made thing to those gathered to see it. The watching is part of the work.
Greek θέατρον (theatron, a place for viewing), from θεᾶσθαι (theasthai, to behold), via Latin theatrum and Old French theatre; the two modern spellings both name exactly the same place.
A place made for showing a made thing to those gathered to see it. The watching is part of the work, whichever of the two spellings is used.