conventicle
A secret, unauthorized or illegal religious meeting.
[I]f when Luther firſt began to teach new doctrine, the catholiks at that time had not vouchſafed to giue him the hering, but had auoided his prechings & preuy couenticles, ther had not bin now in the worlde, either Lutheran, Swinglian, Calueniſt, Puritan, Anabaptiſt, Trinetarie, Family of loue, Adamite, or the lyke: whereof now there are ſo many thouſands abroad, al ſpringing of that firſt ſecte, and troubling at this day the whole worlde, […]
The place where such a meeting is held.
A Quaker meetinghouse.
Where it comes from
From Late Middle English conventicle, conventicule (“a gathering, meeting (especially a secret or unlawful one); (derogatory) a church”), from Latin conventiculum (“assembly; meeting (or the place involved); association”), from conventus (“assembled, convened”) + -culum (suffix forming noun diminutives), perfect passive participle of conveniō (“to assemble, convene, meet together”), from con- (“together, with”) (ultimately from Proto-Indo-European *ḱóm (“along, at, next to, with”)) + veniō (“to approach, come”) (ultimately from Proto-Indo-European *gʷem- (“to step”) + *-yéti (suffix forming intransitive, imperfective verbs)).
Adapted from the Wiktionary entry conventicle (CC BY-SA 4.0).