placard (n.)youdaoicibaDictYouDict[placard 词源字典]
late 15c., "formal document authenticated by an affixed seal," from Middle French placquard "official document with a large, flat seal," also "plate of armor," from Old French plaquier "to lay on, cover up, plaster over," from Middle Dutch placken "to patch (a garment), to plaster," related to Middle High German placke "patch, stain," German Placken "spot, patch." Meaning "poster" first recorded 1550s in English; this sense is in Middle French from 15c.[placard etymology, placard origin, 英语词源]