Definify.com
Webster 1913 Edition
Faithless
Faith′less
,Adj.
 1. 
Not believing; not giving credit. 
Be not 
faithless
, but believing. John xx. 27.
2. 
Not believing on God or religion; specifically, not believing in the Christian religion. 
Shak.
 3. 
Not observant of promises or covenants. 
4. 
Not true to allegiance, duty, or vows; perfidious; trecherous; disloyal; not of true fidelity; inconstant, as a husband or a wife. 
A most unnatural and 
– faithless 
service. Shakespeare
Faith′less-ly
, adv.
Faith′less-ness
, Noun.
Webster 1828 Edition
Faithless
FA'ITHLESS
, a.1.
  Without belief in the revealed truths of religion; unbelieving.O faithless generation.  Math 18.
2.
  Not believing; not giving credit to.3.
  Not adhering to allegiance or duty; disloyal; perfidious; treacherous; as a faithless subject.4.
  Not true to a master or employer; neglectful; as a faithless servant.5.
  Not true to the marriage covenant; false; as a faithless husband or wife.6.
  Not observant of promises.7.
  Deceptive.Yonder faithless phantom.
Definition 2025
faithless
faithless
English
Adjective
faithless (comparative more faithless, superlative most faithless)
-  Lacking faith; lacking belief in something.
-  1970, Margaret Wade Campbell Deland, Old Chester Days, p. 58:
- "You're so faithless about pills," he said, "that I'm not going to give you any."
 
 
-  1970, Margaret Wade Campbell Deland, Old Chester Days, p. 58:
- Not believing in God, religion, or a comparable ideology.
-  Unfaithful; not of true fidelity; inconstant, as a husband or a wife.
-  1996, Frederick Ahl, Hanna Roisman, The Odyssey re-formed, p. 283:
- Menelaus, who fought to recover his faithless wife, has clearly rooted himself in Sparta for the remainder of his life...
 
 
-  1996, Frederick Ahl, Hanna Roisman, The Odyssey re-formed, p. 283:
- Not observant of promises or covenants.
- Not true to allegiance, duty, or vows; perfidious; treacherous; disloyal.
- Serving to disappoint or deceive; delusive; unsatisfying.