ˈfāthlə̇s adjective
Etymology: Middle English feithles, from feith faith + -les -less
1. archaic : not believing : not giving credence
2.
a. archaic : not believing in God or religion
b. : being without a faith : lacking strong convictions
we live in a skeptical and faithless time
3. : false to promises or agreements : not true to allegiance or duty : perfidious , treacherous , disloyal
few of its teachers … have been faithless to their society — C.W. de Kiewiet
he abandoned one wife and was faithless to another — J.R.Green
: inconstant , fickle
she had been too successful, and a faithless public was tired of her — Carl Van Vechten
4.
a. : not to be relied on : unstable , erratic
they are at the mercy of an unseen instructor who can simulate violent weather and faithless machinery — Time
b. : not conforming to a standard or to an original : not true or accurate
the disc has a heavy surface and the tone is faithless — Edward Sackville-West & Desmond Shawe-Taylor
Synonyms:
false , disloyal , traitorous , treacherous , perfidious : faithless applies to any lack of adherence or devotion to a vow, pledge, allegiance, or loyalty
the faithless conduct of the allies toward this dethroned monarch, who, after giving himself generously up to their mercy, was consigned to an ignoble and cruel banishment — W.M.Thackeray
a woman who has been deserted by her lover will make a straw effigy of the faithless gallant — J.G.Frazer
false may center attention on the fact of failing to be true, reasons ranging from fickle negligence to cold treachery
from the first hour of Edward's rule the threads of his diplomacy ran over Europe in almost inextricable confusion. And to all who dealt with him he was equally false and tricky — J.R.Green
men, when they're false, and try to deceive young girls, and are playing their own wicked game with them, do not like to be bothered about such things — Anthony Trollope
disloyal indicates lack of complete faith, loyalty, and adherence to a person, cause, or country
they had already assumed a tone in their correspondence which must have seemed often disloyal, and sometimes positively insulting, to the governor — J.L.Motley
the disloyal subject who had fought against his rightful sovereign — T.B.Macaulay
traitorous applies to committing, countenancing, or contemplating actual treason or similar serious betrayal
traitorous generals collaborating with the enemy
charged with traitorous contempt of the emperor — S.T.Coleridge
treacherous is wider and less specific than traitorous; it may refer to any serious betrayal or inclination to betray or to anything likely to bring sudden peril or disaster unless one is quite wary
thy kin of the days of old were an evil and treacherous folk, and they lied and murdered for gold — William Morris
lighthouses were placed on treacherous parts of the coast — Lewis Mumford
perfidious may add to faithless implications of a base incapacity for fidelity; the word now seems rather declamatory or oratorical
betrayed by his perfidious allies
a perfidious violation of a treaty
perifidious Mrs. Albion who had her spouse, Albion I, murdered by a lover acquired for the purpose — Claudia Cassidy