Wiktionary
untruest
a. (en-superlative of: untrue)
Usage examples of "untruest".
Sir, said Balin, me forthinketh of your displeasure, for this same lady was the untruest lady living, and by enchantment and sorcery she hath been the destroyer of many good knights, and she was causer that my mother was burnt, through her falsehood and treachery.