Mendacious comes from the Latin word mendāx, meaning “lying” or “deceitful.” In English, it has been used since the early 17th century to describe someone or something that is untruthful or prone to lying. Mendacity can be found in many different contexts, from personal relationships and politics to business and finance. Today, mendacious remains a commonly used word in English, and is often associated with deception, dishonesty, and falsehood.