Law. a statement of grievance made to a court for the purpose of asking redress.
3.
a lament; lamentation.
Origin: 1175–1225; ME < MF < L planctus a striking or beating (the breast) in grief, equiv. to plang(ere) to beat, strike, mourn for + -tus, suffix of v. action
[Middle English, from Old French plainte, from Latin plānctus, lament, from past participle of plangere, to strike one's breast, lament; see plāk-2 in Indo-European roots.]
c.1225, "expression of sorrow," from O.Fr. pleint, from L. planctus "lamentation, beating," from plangere "to lament, to strike" (see plague). Connecting notion probably via beating one's breast in grief.