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 with. 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)
ally is generally used in the passive form or reflexively.
Origin: oe. Alien, OF. Alier, f. Alier, fr. L. Alligare to bind to; ad – ligare to bind. Cf. Alligate, alloy, Allay, ligament.