conventicle (n.)

late 14c., "an assembly or gathering," from Latin conventiculum "a small assembly," diminutive of conventus "assembly," originally past participle of convenire "unite, be suitable, agree, assemble," from assimilated form of com "with, together" (see con-) + venire "to come" (from PIE root *gwa- "to go, come").

Conventiculum in Church Latin was used of Christian meetings for worship, but in Medieval Latin and later in Middle English the equivalent word took on a pejorative sense, "illicit meeting," of Lollards, malcontents, etc. (late 14c.) and was used disparagingly of a church or religious house; in Protestant England the meaning "a meeting of dissenters for religious worship" dates to 1590s.