We don't have synonyms for backstabs yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are backstage, backstairs and backstair.
(v) :
(transitive) 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.
(v) :
(transitive) 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.