faithless, false, disloyal, traitorous, treacherous, perfidious mean untrue to what should command one's fidelity or allegiance. faithless applies to any failure to keep a promise or pledge or any breach of allegiance or loyalty.
//faithless allies false stresses the fact of failing to be true in any manner ranging from fickleness to cold treachery.
// betrayed by false friends disloyal implies a lack of complete faithfulness to a friend, cause, leader, or country.
//disloyal to their country traitorous implies either actual treason or a serious betrayal of trust.
//traitorous acts punishable by death treacherous implies readiness to betray trust or confidence.
// a treacherous adviser perfidious adds to faithless the implication of an incapacity for fidelity or reliability.
// a perfidious double-crosser

faithless, disloyal, and traitorous mean not being true to something that has a right to a person's loyalty. faithless is used when a person breaks a promise or pledge to remain loyal to someone or something.
// Our faithless friends left us at the first sign of trouble. disloyal is used when a person is unfaithful to someone or something that has the right to expect loyalty.
// The disloyal citizens will be punished. traitorous is used for actual treason or a betrayal of trust.
// The traitorous soldier was giving secrets to the enemy.