mendacious (adj.)
1610s, from Middle French mendacieux, from Latin mendacium "a lie, untruth, falsehood, fiction," from mendax (genitive mendacis) "lying, deceitful," from menda "fault, defect, carelessness in writing," from PIE root *mend- "physical defect, fault" (see amend (v.)). The sense evolution of Latin mendax was influenced by mentiri "to speak falsely, lie, deceive." Related: Mendaciously; mendaciousness.