al·ly 
(ə-lī, ălī)
(ə-lī, ălī)v. al·lied, al·ly·ing, al·lies
v.tr.
1. To place in a friendly association, as by treaty: Italy allied itself with Germany during World War II.
2. To unite or connect in a personal relationship, as in friendship or marriage.
v.intr.
To enter into an alliance: Several tribes allied to fend off the invaders.
n. (ălī, ə-lī)pl. al·lies
1. One that is allied with another, especially by treaty: entered the war as an ally of France.
2.
a. One in helpful association with another: legislators who are allies on most issues. See Synonyms at partner.
b. An animal that cooperates with another animal of the same species in an alliance.
3. Allies
a. 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.
b. The nations, primarily Great Britain, France, the Soviet Union, and the United States, allied against the Axis during World War II.
[Middle English allien, from Old French alier, from Latin alligāre, to bind to; see ALLOY.]