given to or characterized by deception or falsehood or divergence from absolute truth
Liza wasn't about to fall for the unrealistic claims being touted by the mendacious car salesman.
"Don Draper, the creative ad man extraordinaire on 'Mad Men,' is so deeply flawed that his likability and his possible redemption are seriously in question. A man whose entire life, including his name, is a lie, Draper is a cunning man in a mendacious, predatory world of images." — From an article by Neal Gabler in the Chicago Tribune, April 11, 2010
"Mendacious" and "lying" have very similar meanings, but the two are not interchangeable. "Mendacious" is more formal and literary, suggesting a deception harmless enough to be considered bland. "Lying" is more blunt, accusatory, and often confrontational. You might yell, "You lying rat!" in an argument, but you would most likely stick to the more diplomatic, "Aren’t you being somewhat mendacious?" in a business meeting. "Mendacious" can also imply habitual untruthfulness, whereas "lying" is more likely to be used to identify specific instances of dishonesty.
I would like to know the origin of the word... this great fantastic word, walking the earth in all its awesomeness