ally

American Heritage® Dictionary of the English Language, Fourth Edition

1. v. To place in a friendly association, as by treaty: Italy allied itself with Germany during World War II.
2. v. To unite or connect in a personal relationship, as in friendship or marriage.
3. v. To enter into an alliance: Several tribes allied to fend off the invaders.
4. n. One that is allied with another, especially by treaty: entered the war as an ally of France.
5. n. One in helpful association with another: legislators who are allies on most issues. See Synonyms at partner.
6. n. 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.
7. n. The nations, primarily Great Britain, France, the Soviet Union, and the United States, allied against the Axis during World War II.

Century Dictionary and Cyclopedia

1. To unite by marriage, treaty, league, or confederacy; connect by formal agreement: generally used in the passive or with reflexive pronouns.
2. To bind together; connect, as by resemblance or friendship.
3. To join or unite; enter into alliance.
4. n. One united or associated with another by kinship, treaty, or league; a confederate; more particularly, a sovereign or state connected with another by league offensive and defensive, or a subject or citizen of such sovereign or state.
5. n. An auxiliary; an associate or friend.
6. n. In zoology, an animal more or less closely related to another in respect to morphological characters, and placed in the same alliance (which see). Synonyms Associate, Friend, Companion, etc. See associate.
7. n. A former spelling of alley.
8. n. See alley.

Wiktionary

1. v. transitive To unite, or form a connection between, as between families by marriage, or between princes and states by treaty, league, or confederacy
2. v. transitive To connect or form a relation between by similitude, resemblance, friendship, or love.
3. n. One united to another by treaty or league; — usually applied to sovereigns or states; a confederate.
4. n. Anything associated with another as a helper; an auxiliary.
5. n. Anything akin to another by structure, etc.
6. n. taxonomy A closely related species, usually within the same family.
7. n. Alternative form of alley. (a glass marble or taw)

GNU Webster's 1913

1. v. 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.
2. v. To connect or form a relation between by similitude, resemblance, friendship, or love.
3. n. obsolete A relative; a kinsman.
4. n. One united to another by treaty or league; -- usually applied to sovereigns or states; a confederate.
5. n. Anything associated with another as a helper; an auxiliary.
6. n. Anything akin to another by structure, etc.
7. n. See alley, a marble or taw.

WordNet 3.0

1. v. become an ally or associate, as by a treaty or marriage
2. n. a friendly nation
3. n. an associate who provides cooperation or assistance