a person who instigated or took part in the September Massacre
Word origin
[1830–40; september + -ist, modeled on Pg setembrista (with reference to the revolution of September 1836 in Portugal); r. earlier septembrizer ‹ F septembriseur]This word is first recorded in the period 1830–40. Other words that entered Englishat around the same time include: ante, format, isometric, paraffin, rococo