1610s, "word of honor," especially "promise by a prisoner of war not to escape if allowed to go about at liberty, or not to take up arms again if allowed to return home," from French parole "word, speech" (in parole d'honneur "word of honor") from Vulgar Latin *paraula "speech, discourse," from Latin parabola "comparison," from Greek parabole "a comparison, parable," literally "a throwing beside," hence "a juxtaposition" (see parable). Sense of "conditional release of a prisoner before full term" is attested by 1908 in criminal slang.
1716, from parole (n.). Originally it was what the prisoner did ("pledge"), but this sense is obsolete; its transitive meaning "put on parole, allow to go at liberty on parole" is attested by 1782. Meaning "release (a prisoner) on his own recognizance" is by 1888. Related: Paroled; paroling.