noun
joiner
JOY-ner/ˈdʒɔɪnər/
A person who readily becomes a member of groups.
The enthusiastic joiner signs up at several community booths.

Etymology
The joining root and person-forming ending describe someone who unites with others. In this sense, the emphasis is on habitually becoming a member of clubs or societies.
In context
I've never been much of a joiner
More examples
- She described herself as a joiner who enjoyed group activities.
- The town’s enthusiastic joiners signed up for every committee.
- Unlike her brother, she had never been a joiner.
Forms
joiner · joiners
Similar words
- member
- A member belongs to a group; a joiner habitually seeks out groups to join.
- participant
- A participant takes part; joiner emphasizes a tendency to sign up or affiliate.