Adjective
1. not true to duty or obligation or promises;
"an unfaithful lover"2. having sexual relations with someone other than your husband or wife, or your boyfriend or girlfriend;
"her husband was unfaithful"3. deliberately and abominably disloyal or likely to betray trust or confidence;
"the faithless Benedict Arnold""a lying traitorous insurrectionist"4. not trustworthy;
"an unfaithful reproduction"