exo-

External; from outside.

Greek exō, outside.

The great majority of words here are in modern technical and scientific usage; exceptions are exotic, which derives via Latin from Greek exōtikos, foreign, and exogamy (Greek gamos, marriage), the custom of marrying outside a community, clan, or tribe. Some examples of technical terms are exoskeleton, a rigid external covering for the body in some invertebrate animals; exothermic, of a chemical reaction or process that is accompanied by the release of heat; exogenous, developing from external factors; exobiology, the branch of science that deals with the possibility and likely nature of life on other planets or in space.

Its opposite is endo‑; see also ecto‑. Words such as exorbitant or exonerate instead contain Latin ex‑ (see ex‑¹); some, such as exodus or exorcize, come from Greek (see ex‑²).