c.1215, "lawsuit," from Anglo-Fr.
plai (c.1170), O.Fr.
plait "lawsuit, decision, decree" (842), from M.L.
placitum "lawsuit," in classical L., "opinion, decree," lit. "that which pleases, thing which is agreed upon," properly neut. pp. of
placere (see
please). Sense development seems to be from "something pleasant," to "something that pleases both sides," to "something that has been decided." Meaning "a pleading, an agreement in a suit" is attested from c.1381.
Plea bargaining is first attested 1963.
Common pleas (c.1215) originally were legal proceedings over which the Crown did not claim exclusive jurisdiction (as distinct from
pleas of the Crown); later "actions brought by one subject against another."