* Membership: This is the most common and general abstract noun for "member". It refers to the state of being a member of a group or organization.
* Affiliation: This refers to the connection or association with a group or organization.
* Participation: This emphasizes the act of taking part in a group or activity.
* Belonging: This refers to the feeling of being part of a group or community.
The best abstract noun to use will depend on the specific meaning you want to convey.