Conventicle

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

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.

a building for religious assembly (especially Nonconformists, e.g., Quakers)