【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.