noun

1. an allying or being allied; specif., a union or joining, as of families by marriage
2. a close association for a common objective, as of nations, political parties, etc.
3. the agreement made for such an association
4. the countries, groups, etc. forming such a connection
5. similarity or relationship in characteristics, structure, etc.; affinity

Etymology: ME aliaunce < OFr aleiance < alier: see ally