Definition of Septembrist in US English:

Septembrist

noun

historical
  • 1A participant in or advocate of the massacre of political prisoners that took place in Paris on 2–6 September 1792.

  • 2A participant in or supporter of the successful Portuguese insurrection of September 1836, in favour of the restoration of the constitution of 1822.

Origin

Late 18th century; earliest use found in Helen Maria Williams (1761–1827), writer. From September + -ist. With sense 1 compare French septembriste and septembriseur.