Origin and usage
The adjective mendacious comes from the Latin ‘mendax’ or ‘mendac-‘ meaning ‘lying’ plus the suffix -ious. It was first used in English in the early 17th century.
The adjective mendacious, which is marked as ‘very formal’ in Macmillan Dictionary, is a rather infrequent word with around 2250 citations in the huge corpus we use to compile the dictionary. As well as being used to describe someone who is a habitual liar, mendacious also means used about statements or information that are deliberately false. In this meaning it is likely to be followed by nouns such as drivel, propaganda, nonsense, pretext and allegation. The adverb mendaciously often modifies the verb ‘claim’. The related noun is mendacity.
“The British Crown mendaciously claimed that the ‘evil-minded’ mischievous Gordon threatened international harmony and required punishment.”
“This in no way implies that he is a mendacious liar.”
“This headline is, to say the least, misleading, if not downright mendacious.”
crooked, deceitful, duplicitous, shifty