posterior adj.

word-forming element meaning "after," from Latin post "behind, after, afterward," from *pos-ti (source also of Arcadian pos, Doric poti "toward, to, near, close by;" Old Church Slavonic po "behind, after," pozdu "late;" Lithuanian pas "at, by"), from PIE *apo- (source also of Greek apo "from," Latin ab "away from" see apo-).

late 14c., posteriorite, "condition of occurring later in time, state of being subsequent," from Old French posteriorite (Modern French postériorité), from Medieval Latin posterioritatem (nominative posterioritas), from Latin posterior "later" (see posterior (adj.)).

mid-15c., posthumus, "born after the death of the originator" (author or father), from Late Latin posthumus, from Latin postumus "last," especially "last-born," superlative of posterus "coming after, subsequent" (see posterior). Altered in Late Latin by association with Latin humare "to bury," suggesting death; the one born after the father is in the ground obviously being his last. An Old English word for this was æfterboren, literally "after-born." Related: Posthumously.