We don't have synonyms for massacer yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are massage, massacre and massager.
(n) :
Archaic form of massacre. [The killing of a considerable number (usually limited to people) where little or no resistance can be made, with indiscriminate violence, without necessity, and/or contrary to civilized norms.]
(v) :
Archaic form of massacre. [(transitive) To kill in considerable numbers where little or no resistance can be made, with indiscriminate violence, without necessity, and contrary to civilized norms. (Often limited to the killing of human beings.)]
(n) :
Archaic form of massacre. [The killing of a considerable number (usually limited to people) where little or no resistance can be made, with indiscriminate violence, without necessity, and/or contrary to civilized norms.]
(v) :
Archaic form of massacre. [(transitive) To kill in considerable numbers where little or no resistance can be made, with indiscriminate violence, without necessity, and contrary to civilized norms. (Often limited to the killing of human beings.)]