The Collaborative International Dictionary of English v.0.48:

Conventicle \Con*ven"ti*cle\, n. [L. conventiculum, dim. of
   conventus: cf. F. conventicule. See Convent, n.]
   1. A small assembly or gathering; esp., a secret assembly.
      [1913 Webster]

            They are commanded to abstain from all conventicles
            of men whatsoever. --Ayliffe.
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   2. 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.
      [1913 Webster]

            The first Christians could never have had recourse
            to nocturnal or clandestine conventicles till driven
            to them by the violence of persecution. --Hammond.
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            A sort of men who . . . attend its [the curch of
            England's] service in the morning, and go with their
            wives to a conventicle in the afternoon. --Swift.
      [1913 Webster]

WordNet (r) 3.0 (2006):

conventicle
    n 1: a secret unauthorized meeting for religious worship
    2: a building for religious assembly (especially Nonconformists,
       e.g., Quakers) [syn: conventicle, meetinghouse]