An item possessed by a family, or other group, that is passed down through the generations of that group. This could be a noun, as in, "This batleth is an heirloom of House Mogh". Or this could be a "be verb", as in "be an heirloom", a state that a specific object could be in: "I see the House Mogh heirloom batleth". "The batleth is an heirloom".