extra-

Outside; beyond.

Latin extra, outside.

Extraordinary comes from the Latin phrase extra ordinem, outside the normal course of events; an extramural course of study derives from Latin extra muros, outside the walls; extravagant from Latin vagari, wander; extraneous from extraneus, external; something extramarital occurs outside marriage, especially a sexual relationship.

Technical terms derived from the same source include extrapolate (extra‑ plus the second part of interpolate), to infer or estimate by extending or projecting known information; extraterrestrial, of or from outside the earth or its atmosphere (or a hypothetical or fictional being from outer space, especially an intelligent one); extravehicular, relating to work performed outside a spacecraft; extravasation (Latin vas, vessel), the escape of fluids from the vessels that naturally contain them.

A number of words contain Latin ex‑ instead, for example extract and extradition; see ex‑¹. The opposite is intra‑.