The Collaborative International Dictionary of English v.0.48:
Ally \Al*ly"\, v. t. [imp. & p. p. Allied; p. pr. & vb. n.
Allying.] [OE. alien, OF. alier, F. alier, fr. L. alligare
to bind to; ad + ligare to bind. Cf. Alligate, Alloy,
1. 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
O chief! in blood, and now in arms allied. --Pope.
2. To connect or form a relation between by similitude,
resemblance, friendship, or love.
These three did love each other dearly well,
And with so firm affection were allied. --Spenser.
The virtue nearest to our vice allied. --Pope.
Note: Ally is generally used in the passive form or