Ally \Al*ly"\, n.; pl. Allies. [See Ally, v.]

1. A relative; a kinsman. [Obs.]

--Shak.

2. One united to another by treaty or league; -- usually applied to sovereigns or states; a confederate.

The English soldiers and their French allies. --Macaulay.

3. Anything associated with another as a helper; an auxiliary.

Science, instead of being the enemy of religion, becomes its ally. --Buckle.

4. Anything akin to another by structure, etc.

Source: Webster's Revised Unabridged Dictionary (1913)