unfaithful

/ˈʌnˌfeɪθfəl/

/ənˈfeɪθfʊl/

When someone is unfaithful, they're disloyal or unreliable. If you don't honor the pledge you made "to help people at all times," you're being unfaithful to the Girl Scout code.

While it's common to use the word unfaithful for people who break their marriage vows, it's a great way to describe someone who's broken any serious promise or neglected an obligation. An elected government official who doesn't keep their promises to voters is an unfaithful public servant. And if your brother refuses to participate in the family's annual Halloween custom of dressing as pirates, you can say he's being unfaithful to the tradition.

Definitions of unfaithful

1. adjective

   not true to duty or obligation or promises
   synonyms:

   inconstant

   likely to change frequently often without apparent or cogent reason; variable

   apostate

   not faithful to religion or party or cause

   perfidious, punic, treacherous

   tending to betray; especially having a treacherous character as attributed to the Carthaginians by the Romans

   untrue

   not true to an obligation or trust

   untrustworthy, untrusty

   not worthy of trust or belief

   antonyms:

   faithful

   steadfast in affection or allegiance

   constant

   steadfast in purpose or devotion or affection

   fast, firm, loyal, truehearted

   unwavering in devotion to a friend or vow or cause

   true

   devoted (sometimes fanatically) to a cause or concept or truth

   true

   consistent with fact or reality; not false

   trustworthy, trusty

   worthy of trust or belief
2. adjective

   having sexual relations with someone other than your husband or wife, or your boyfriend or girlfriend
   synonyms:

   adulterous, cheating, two-timing

   not faithful to a spouse or lover

   antonyms:

   faithful

   not having sexual relations with anyone except your husband or wife, or your boyfriend or girlfriend

   true to

   sexually faithful
3. adjective

   having the character of, or characteristic of, a traitor
   synonyms: faithless, traitorous, treasonable, treasonous

   disloyal

   deserting your allegiance or duty to leader or cause or principle
4. adjective

   not trustworthy
   “an unfaithful reproduction”

   synonyms:

   inaccurate

   not exact