What is caveman's weapon a type of playing card and a group with members?

The term "caveman's weapon" likely refers to a "club," which is a blunt weapon used in prehistoric times. In playing cards, there is a suit called "clubs." Additionally, a "club" can also refer to a group of individuals who share a common interest or activity, such as a book club or sports club. Thus, the Word "club" connects all three concepts.