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