An alliance is a relationship among people, groups, or states that have joined together for mutual benefit or to achieve some common purpose, whether or not an explicit agreement has been worked out among them. That means during times of war, for example, if two countries have an alliance, one will help the other by providing weapons and supplies. Countries that have an alliance, or agreement, help each other out when in need. . a relationship in which people agree to work together; 2 : the state of being joined in some activity or effort the state of being allied Explore obituaries and service times for families served by Alliance Funeral Home and Cremation Center. a relationship in which people agree to work together; 2 : the state of being joined in some activity or effort the state of being allied Alliance Lifetime Mental Health Inc. Find service information, send flowers, and leave memories and thoughts in the Guestbook for your loved one. Definition of alliance noun in Oxford Advanced Learner's Dictionary. Find contact information, view maps, and more. Alliance Lifetime Mental Health Inc.