To harm, ruin, or defame severely or destroy by treachery, slander, libel, or obscure attack.
To murder someone, especially an important person, by a sudden or obscure attack, especially for ideological or political reasons.
to attack someone (especially verbally) unfairly in a deceitful, underhand, or treacherous manner, especially when they're not present in the place or situation that it happens. (as if stabbing them in the back). See backbite.