n.1 a union or agreement to cooperate, esp. of States by treaty or families by marriage. b the parties involved.
2 (Alliance) a political party formed by the allying of separate parties.
3 a relationship resulting from an affinity in nature or qualities etc. (the old alliance between logic and metaphysics).
4 Bot. a group of allied families.
Etymology: ME f. OF aliance (as ALLY(1))