theater

English theater comes from Middle English theater/theatre, from Old French theatre, from Latin theātrum, from Ancient Greek θέᾱτρον (théātron, 'a place for viewing'), itself from θεᾰ́ομαι (theắomai, 'to see, to watch, to observe').

The word has stayed remarkably close to its root sense all along: from Greek 'a place for viewing' to Latin theātrum, through Old French and Middle English, into modern theater — always naming a place built for watching something.

Theater is a doublet of tiatr, meaning the two words descend from the same source but arrived in English by different paths.