1530s, "later in time," from Latin posterior "after, later, behind," comparative of posterus "coming after, subsequent," from post "after" (see post-). Meaning "situated behind, later in position than another or others" is from 1630s. Related: Posterial.
"buttocks, the hinder parts of the body of a human or animal," euphemistic, 1610s, from posterior (adj.). Earlier it meant "those who come after, posterity" (1530s). Compare Lithuanian pasturas "the last, the hindmost," from pas "at, by." Middle English had partes posterialle "the buttocks" (early 15c.), from Latin posterioras with a change of suffix.
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.
"to render prone," specifically to rotate the hand so that its palmar surface faces in the same direction as the posterior surface of the ulna, 1819, from Late Latin pronatus, past participle of pronare "to bend forward," from pronus "prone" (see prone). Related: Pronated; pronator; pronating. As an adjective, "bent into a prone position," by 1848.
1540s, "flesh or meat of the belly" (a sense now obsolete), from Latin abdomen "the belly," a word of unknown origin, Perhaps [OED, Watkins] from abdere "conceal" (from ab "off, away" + PIE root *dhe- "to set, put"), with a sense of "concealment of the viscera," or else "what is concealed" by proper dress. De Vaan, however, finds this derivation "unfounded." Anatomical sense "part of the mammalian body between the diaphragm and the pelvis" is from 1610s. Zoological sense of "posterior division of the bodies of arthropods" by 1725.
Old English botm, bodan "ground, soil, foundation, lowest or deepest part of anything," from Proto-Germanic *buthm- (source also of Old Frisian boden "soil," Old Norse botn, Dutch bodem, Old High German bodam, German Boden "ground, earth, soil"). This is perhaps from PIE root *bhudhno- "bottom" (source also of Sanskrit budhnah, Avestan buna- "bottom," Greek pythmen "foundation," Latin fundus "bottom, piece of land, farm," Old Irish bond "sole of the foot").
Meaning "fundamental character, essence" is from 1570s; to get to the bottom of some matter is from 1773. Meaning "posterior of a person" (the sitting part) is from 1794. Bottoms up as a call to finish one's drink is from 1875. Bottom dollar "the last dollar one has" is from 1857. To do or feel something from the bottom of (one's) heart is from 1540s. Bottom-feeder, originally of fishes, is from 1866.