noun
1.
the act of allying or state of being allied.
2.
a formal agreement or treaty between two or more nations to cooperate for specific purposes.
3.
a merging of efforts or interests by persons, families, states, or organizations:
an alliance between church and state.
4.
the persons or entities so allied.
5.
marriage or the relationship created by marriage between the families of the spouses.
6.
correspondence in basic characteristics; affinity:
the alliance between logic and metaphysics.