1 [count] a : an established organization ▪ an educational/academic institution ▪ banks and other financial institutions ▪ an institution of higher learning b : a place where an organization takes care of people for a usually long period of time ▪ She committed herself to a mental institution. [=a hospital for people with mental or emotional problems] ▪ a correctional institution [=a prison]
2 [count] a : a custom, practice, or law that is accepted and used by many people ▪ Family visits are a Thanksgiving institution. ▪ She's not interested in the institution of marriage. ▪ the institution of slavery b : someone or something that is very well known and established in a particular field or place ▪ He is an institution in local politics. [=he has participated in local politics for such a long time that people consider him to be a regular part of local politics] ▪ The play has become something of an institution on Broadway.
3 [noncount] : the act of beginning or creating something (such as a new law, rule, or system) : the act of instituting something ▪ the institution of new rules and regulations