an arrangement in which two or more countries, groups etc agree to work together to try to change or achieve something

联盟，结盟:

Britain's military alliance with her NATO partners

英国和它北约伙伴的军事联盟

the possibility of a political alliance between the two parties

两党政治联盟的可能性

The companies have formed an alliance to market the product.

各家公司联手将该产品推向市场。

a group of two or more countries, groups etc who work together to achieve something

结盟团体，同盟:

independent organizations and alliances

独立组织和联盟

in alliance (with sb / sth), if two groups, countries etc are in alliance, they work together to achieve something or protect each another

（与某人/某物）联盟（联手）:

Relief workers in alliance with local charities are trying to help the victims.

救济人员与当地慈善机构联合起来，设法帮助那些灾民。

[formal] a close relationship, especially a marriage, between people

〔人们间的〕亲密关系;〔尤指〕联姻