Dishonest, deceitful, mendacious, lying, untruthful are comparable especially when applying to persons, their utterances, and their acts and meaning deficient in honesty and unworthy of trust or belief.
Dishonest may apply to any breach of honesty or trust (as by lying, deceiving, stealing, cheating, or defrauding).
Deceitful usually implies the intent to mislead or to impose upon another in order to obscure one’s real nature or actual purpose or intention, or the true character of something offered, given, or sold; it therefore usually suggests a’ false or specious appearance, indulgence in falsehoods, cheating, defrauding, or double-dealing.
Mendacious is typically more formal than, often less derogatory than, but otherwise closely equivalent to lying, the ordinary, direct, unequivocal word.
As applied to persons mendacious more often suggests the habitude of deceit while lying suggests guilt in respect to a particular instance; thus, one might describe a person as mendacious with primary reference to his character or habit but would ordinarily prefer lying when a particular instance is in view.
Untruthful is often used in place of mendacious or lying as a slightly less brutal word; however, the term distinctively implies lack of correspondence between what is said or represented and the facts of the case or the reality, and is often applied to statements, accounts, reports, or descriptions with little stress on dishonesty or intent to deceive.