English 'amphitheater' from Greek 'amphithéatron' — literally 'theater on both sides,' from 'amphi-' (around) + 'théatron' (viewing place).
An open circular or oval building with a central space for performances or combat, surrounded by tiers of seats; any similarly shaped area.
From Latin "amphitheātrum," from Greek "ἀμφιθέατρον" (amphithéatron), a compound of "ἀμφί" (amphí, "on both sides, around") and "θέατρον" (théatron, "a place for viewing"), from "θεᾶσθαι" (theâsthai, "to view, to behold"). The prefix "amphí" derives from PIE *h₂m̥bʰi ("around, on both sides"), which also produced Latin "ambi-" ("around," as in "ambiguous," "ambient"), Old English "ymbe" ("around"), and Sanskrit "abhí" ("toward, around"). The root "théatron" comes from PIE *dʰeh₁- ("to set, to place"), via the Greek semantic development from "placing" to "observing" to "a place of observation
The Colosseum in Rome (completed 80 CE) is the most famous amphitheater and could hold 50,000 to 80,000 spectators. The word 'amphitheater' distinguishes the Roman oval design (seating on ALL sides) from the Greek 'theater' (semicircular, with seating on only one side). The prefix 'amphi-' (both sides) also appears in 'amphibian' (living on both land and water) and 'amphora' (a jar