"bond money, security given to obtain the release of a prisoner," late 15c., a sense that apparently developed from that of "temporary release (of an arrested person) from jail" (into the custody of another, who gives security for future appearance at trial), which is recorded from early 15c. That seems to have evolved from the earlier meanings "captivity, custody" (late 14c.), "charge, guardianship" (early 14c.).

The word is from Old French baillier "to control, to guard, deliver" (12c.), from Latin baiulare "to bear a burden," from baiulus "porter, carrier, one who bears burdens (for pay)," which is of uncertain origin; perhaps it is a borrowing from Germanic and cognate with the root of English pack, or perhaps from Celtic. De Vaan writes that, in either case, "PIE origin seems unlikely."

To go to (or in) bail "be released on bail" is attested from mid-15c. In late 18c. criminal slang, to give leg bail meant "to run away."

Middle English baylle, "wall enclosing an outer court" of a castle, fortified city, etc. (c. 1200 in Anglo-Latin, late 13c. in place-names), a variant of bail, from Old French bail "stake, palisade, brace," which is of unknown origin, perhaps ultimately connected to Latin bacula "sticks," on notion of "stakes, palisade fence."

The word was extended to mean the outer court itself (early 14c.). Hence Old Bailey, seat of Central Criminal Court in London, so called because it stood within the ancient bailey of the city wall. The surname Bailey usually is from Old French bailli, a later form of baillif (see bailiff). Bailey's, the Irish whiskey- and cream-based liqueur, was introduced in 1974 and said to have been named for the historic Bailey's Hotel in London.

mid-15c., "district of a bailiff, jurisdiction of a royal officer or under-sheriff," a contraction of baillifwik, from bailiff (q.v.) + Middle English wik, from Old English wic "village" (see wick (n.2)). The figurative sense of "one's natural or proper sphere" is by 1843.

server of writs, maker of arrests, etc., "A bailiff of the meanest kind; one that is employed in arrests" [Johnson], c. 1600, from bum (n.1) "arse" + bailiff, because he was always felt to be close behind. OED compares the French equivalent pousse-cul.