conventicle
Concise Oxford English Dictionary © 2008 Oxford University Press:
conventicle /kənˈvɛntɪk(ə)l/
▶noun historical a secret or unlawful religious meeting, typically of nonconformists.
– origin ME: from L. conventiculum ‘(place of) assembly’, dimin. of conventus ‘assembly, company’, from convenire (see convene).
'conventicle' also found in these Oxford entries:

