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1827, originally short for ex-Catholic; ultimately from Latin ex (see ex-). Since 1929 as abbreviation for ex-wife, ex-husband, etc. Also used in some commercial senses for "from, out of."
word-forming element, in English meaning mainly "out of, from," but also "upwards, completely, deprive of, without," and "former;" from Latin ex "out of, from within," from PIE *eghs "out" (cf. Gaulish ex-, Old Irish ess-, Old Church Slavonic izu, Russian iz). In some cases also from Greek cognate ex, ek. PIE *eghs had comparative form *eks-tero and superlative *eks-t(e)r-emo-.
Outside; out of; away from: excementosis.
A former wife or husband, girlfriend or boyfriend, etc: He introduced his ex rather casually, considering they were together 27 years (1929+)