[C] a large organization that has a particular kind of work or purpose

机构，团体:

the Government and other political institutions

政府和其他政治机构

powerful institutions such as world banks

诸如世界银行之类的权力机构

the Institution of Electrical Engineers

电机工程师学会

[C] an important system of organization in society that has existed for a long time

〔由来已久的〕制度:

social institutions such as the family and religion

家庭和宗教这一类社会制度

The scandal threatened to undermine the institution of the Presidency.

丑闻可能危及总统制度。

[C] a building that people are sent to when they need to be looked after, for example old people or children with no parents – often used to show disapproval

慈善机构; 社会福利机构〔常含贬义〕:

I was determined not to put my mother in an institution.

我决心不送我母亲到养老院。

a mental institution (=for the mentally ill)

精神病院

[U] when something is started or introduced, especially something relating to the law or politics

〔尤指与法律或政治有关的〕开创; 制定:

the institution of divorce proceedings

离婚诉讼的制定

be an institution, if a person, place, event etc is an institution, they have been an important part of a place for a very long time – often used humorously

〔已长期成为某地〕重要（出名）的人（地点，事件等）〔常为幽默用法〕:

The British pub isn't just somewhere to drink – it's an institution.

这家英式酒吧不仅仅是喝酒的地方 — 它享有盛名。