Untrue
Part of speech: adjective
Definition: False; not true.
Example sentence: Emotions can certainly be misleading: they can fool you into believing stuff that is definitely, demonstrably untrue.
Unfaithful
Part of speech: adjective
Definition: not having religious faithnot keeping good faith; disloyal; not faithfulnot honest or uprightof a translation: incorrectadulterous
Example sentence: Nobody could pile on the applesauce like Mickey. He was the best liar in the world - well, Frank Sinatra can tell a good story, too, but I don't believe he was ever unfaithful to me.