postern

Origin

The noun is derived from Middle English postern, posterne (“side door or gate; small entranceway; hidden or secret door or passage”), from Late Latin posterna, and from its likely etymon Anglo-Norman posterne and Old French posterne (“hidden exit from a fortified building; back door; small door”) (modern French poterne), a variant of posterle (“back door or passage”) (although this is attested later), possibly also influenced by Latin externus (“external, outward”) and internus (“internal, inward”). Posterle is from Late Latin posterla, posterula (“(small) back door, gate, or way”), from Latin posterus (“coming after, later, next”) (from post (“after; behind”), ultimately from Proto-Indo-European *pós (“afterwards; at, by”)) + -ula (suffix denoting an instrument). The adjective is from an attributive use of the noun.