faithless

From Middle English feithles, equivalent to faith +‎ -less.

faithless (comparative more faithless, superlative most faithless)

1. Lacking faith; lacking belief in something.
   • 1970, Margaret Wade Campbell Deland, Old Chester Days, page 58:

     "You're so faithless about pills," he said, "that I'm not going to give you any."

2. Not believing in God, religion, or a comparable ideology.
3. Unfaithful (said of people, towards their partners)
   • 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 […]

4. Not observant of promises or covenants.
5. Not true to allegiance, duty, or vows

   Synonyms: perfidious, treacherous, disloyal

6. Serving to disappoint or deceive

   Synonyms: delusive, unsatisfying

• faithless elector
• faithlessly
• faithlessness

• flashiest, stalefish