Posterity

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late Middle English: from Old French posterite, from Latin posteritas, from posterus ‘following’.

wiktionary

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Late 14th century, from Middle French posterité, from Latin posteritas, from posterus(“following, coming after”), from post(“after”) (English post-). [1]

Displaced Old English words such as æftergengnes, æfterweardnes, and cnēores.

etymonline

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posterity (n.)

"a person's offspring, descendants collectively," late 14c., posterite, from Old French posterité (14c.), from Latin posteritatem (nominative posteritas) "future, future time; after-generation, offspring;" literally "the condition of coming after," from posterus "coming after, subsequent," from post "after" (see post-). Old English words for this included æftercneoreso, framcynn.