(in a positive sense) Having a sweet and smooth voice; eloquent.
(in a negative sense) Indirect, delivering a message in a way that will make it seem more pleasant to the hearer(s); seductive, persuasive.
Not honest or upright.
Not keeping good faith; disloyal; not faithful.
Negligent or imperfect.
Not faithfully rendering the meaning of the source language; incorrect.
Not having religious faith.
Adulterous.