"bond money," late 15c., a sense that apparently developed from that of "temporary release from jail" (into the custody of another, who gives security), recorded from early 15c. That evolved from earlier meaning "captivity, custody" (early 14c.). From Old French baillier "to control, to guard, deliver" (12c.), from Latin bajulare "to bear a burden," from bajulus "porter," of unknown origin. In late 18c. criminal slang, to give leg bail meant "to run away."