A group whose members share a nature. Also gentle in manner — the same root, since kin and kindness both come from belonging.
Old English gecynd (nature, kind, race) and cynde (natural), both from cynn (kin); a group sharing one nature, and, in the adjective, a gentleness rooted in the same idea of belonging together.
The same root serves a group's shared nature and a gentle manner, because both kinship and kindness begin in belonging together.