- a person who instigated or took part in the September Massacre.
- French history a person who took part in the September Massacre
n.1798 in reference to French history, a participant in the massacre of the political prisoners in Paris, Sept. 2-5, 1792. In French, Septembriseur, hence English Septembriser (1797). Hence also septembrize “assassinate while in custody” (1793).