This is the 8166th most frequent Japanese word.
属し
"属し" (zokushi) means "to belong to" or "to be affiliated with."
In this sentence, '属している' conveys the idea of being a member of or associated with the reading club.
彼はその楽しい読書クラブに属している。
He belongs to the enjoyable reading club.
Here, '属している' indicates association or membership in a peace-supporting organization.
私たちは平和を支持する団体に属しています。
We belong to an organization that supports peace.
In this example, '属している' suggests that the star is part of or included in a constellation.