Joint
United; coupled together in interest; shared between two or more persons; not solitary in interest or action but acting together or in unison. A combined, undivided effort or undertaking involving two or more individuals. Produced by or involving the concurring action of two or more; united in or possessing a common relation, action, or interest. To share common rights, duties, and liabilities.
Additional topics
Law Library - American Law and Legal InformationFree Legal Encyclopedia: Internal Revenue Service - Duties And Powers to Joint will