KKK, Klan, Ku Klux Klan - a secret society of white Southerners in the United States; was formed in the 19th century to resist the emancipation of slaves; used terrorist tactics to suppress Black people

association - a formal organization of people or groups of people; "he joined the Modern Language Association"

Freemasonry, Masonry - Freemasons collectively

National Volunteers Association, Rashtriya Swayamsevak Sangh - a secret all-male organization begun in 1925 to foster nationalism in India's Hindus