Mendaciousness is a complex word that refers to the quality of being deceitful or dishonest. Synonyms for mendaciousness include duplicity, deceitfulness, untruthfulness, falsehood, dishonesty, and insincerity. Duplicity suggests a deliberate attempt to mislead others. Deceitfulness is the quality of being deceptive or misleading. Untruthfulness is the state of being dishonest and untrustworthy. Falsehood refers to a statement or act that is intentionally untrue. Dishonesty implies a lack of integrity or a willingness to deceive. Insincerity indicates a lack of honesty or genuineness in one's words or actions. Each of these synonyms captures a slightly different aspect of mendaciousness but all convey the idea of a lack of truthfulness and honesty.