From Longman Dictionary of Contemporary Englishmurderessmur‧der‧ess /ˈmɜːdərɪs $ ˈmɜːr-/ noun [countable] old-fashioned SCCKILLa woman who murders another person
Examples from the Corpus
murderess• And, most awful of all, was Amy a murderess?• I nearly became a murderess tonight.• Any moment now, one burst of shooting would make Harriet Shakespeare childless and turn the Hare-woman into a murderess.• The concluding song, Murder in the Market, brings a hilarious stanza sung falsetto when the murderess gives her defiant answer.• The murderess is then adopted by the orphaned workers, who unsuspectingly tend her eggs and larvae. 