这些单词均有效忠的含义。相比之下，allegiance多指义务上的忠诚，如公民效忠其国家或王国[1]，如oath of allegiance； 同时其也用于表示政治或原则等方面的忠诚。fealty则专门用于封建王朝封臣或奴隶等对封建主的效忠[2]。fidelity常表示一种强烈的奉献精神，有依附和固执的含义[3]，如：His fidelity to the principles of justice never wavered. 比较之下，loyalty 则更多带有个人关系色彩，表示强烈的个人承诺，具有热爱和献身的含义，常用于对个人、事业、责任或政府的忠诚[4]。
[1 ] “ Obedience owed to the sovereign or government. ” Cf. Daphne Dukelow, The Dictionary of Canadian Law，at p. 37, A Carswell Publication (1991).
[2] " In feudal law, fidelity；allegiance to feudal lord of the manor； the feudal obligation resting upon the tenant or vassal by which he was bound to be faithful and true to his lord, and render him obedience and service. ” Cf. The Publisher's Editorial Staff, Black's law Dictionary, abridged 6th edition, at p. 422, West Publishing Co. (1991).
[3] "Fidelity implies a strong and faithful dedication. " Cf. The Editors of the Reader's Digest, Use the Right Word, at p. 11, The Reader's Digest Association Proprietary Ltd. (1971).
[4] "Faithfulness or allegiance to a person, cause, duty, or government. ”Cf. Bryan A. Gamer, Black's Law Dictionary, 7th edition, at p. 959，West Group (1999).