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).
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