To unite, or form a connection between, as between families by marriage, or between princes and states by treaty, league, or confederacy; -- often followed by to or with.
- To place in a friendly association, as by treaty: Italy allied itself with Germany during World War II.
- To unite or connect in a personal relationship, as in friendship or marriage.
- To enter into an alliance: Several tribes allied to fend off the invaders.
- One that is allied with another, especially by treaty: entered the war as an ally of France.
- One in helpful association with another: legislators who are allies on most issues. See Synonyms at partner.
- The nations allied against the Central Powers of Europe during World War I. They were Russia, France, Great Britain, and later many others, including the United States.
- The nations, primarily Great Britain, France, the Soviet Union, and the United States, allied against the Axis during World War II.