Meaning

noun (United Kingdom) a written statement of the grounds of complaint made to court of law asking for the grievance to be redressed

noun a cry of sorrow and grief

originFrom Middle English plainte, borrowed from Anglo-Norman plainte (“lamentation”), plaint (“lament”), and Old French pleinte (“lamentation”), pleint (“lament”) (modern French plainte), from Medieval Latin plancta (“plaint”), from Latin planctus (“a beating of the breast in lamentation, beating, lamentation”), from Latin plango (“to beat one's breast, to lament”); see plain.

Etymology from Wiktionary, CC BY-SA 3.0