What is Once In Jeopardy?

Legal Definition
A phrase used to express the condition of a person charged with crime, who has once already, by legal proceedings, been put In danger of conviction and punishment for the same offence. See Com. v. Fitzpatrick, 121 Pa. 109, 15 Atl. 466, 1 In R. A. 451, 6 Am. St. Rep. 757. Once quit and cleared, ever quit and cleared. (Scotch, anis quit and clenged, ay quit and clenged.) Skene, de Verb. Sign, voc. "Iter.," ad fin.
-- Black's Law Dictionary
Legal Definition
A plea of former jeopardy for the same offence. See 121 Pa. 109, 6 Am. St. Rep. 757, 1 L. R. A. 451, 15 Atl. 466. See, also, Jeopardy.
-- Ballentine's Law Dictionary