👉 In law, a "copartner" is a person who has an interest in another person's property or business. This can include joint ownership of a business entity, as well as involvement with a company, partnership, or corporation. A copartner may also have a relationship with a partner, such as by being the owner or shareholder of a company. For example, a parent and child might be considered a copartner in a family business, while a parent and spouse might be considered a copartner