Conventicle

Webster's Dictionary of the English Language

·noun A small assembly or gathering; ·esp., a secret assembly.

II. Conventicle ·noun An assembly for religious worship; ·esp., such an assembly held privately, as in times of persecution, by Nonconformists or Dissenters in England, or by Covenanters in Scotland;

— often used opprobriously, as if those assembled were heretics or schismatics.