"elevated part of a Greek city," often the site of original settlement and usually a citadel, 1660s, from Latinized form of Greek akropolis "citadel" (especially, with capital A-, that of Athens), from akros "highest, upper" (from PIE root *ak- "be sharp, rise (out) to a point, pierce") + polis "city" (see polis). The plural would be acropoles.