secret society

noun2

1. •
   A club, fraternal organization, or other association which admits only selected individuals as members, whose meetings and practices are often ritualistic and not public, and which often has the purpose of furthering the social or economic opportunities of its members.

   • Ben had much fun out of it, assuring the other boys that those were the signs and password of a secret society to which he and Sam belonged. — 1879
2. •
   (Singapore) A criminal gang.

   • […] obedience and loyalty were also 'important bywords' to the Ghee Hin, Ghee Hok and Ho Seng secret societies […] — 2023