Definition - A word that has the same function as a preposition, but which comes after the word it governs.

Example -
The in in the phrase the town that he lives in.

Etymology -
The word derives from the Late Latin postpositio, place after.

Oxford English Dictionary -
Its first citation is from 1846:
"In some classes of languages the whole process of formation is carried on by means of postpositions, generally of a known and determinate signification."
(Proceedings of the Philological Society, III., 9)

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