The noun institution has 5 senses (first 4 from tagged texts)
1. (26) institution, establishment -- (an organization founded and united for a specific purpose)
2. (2) institution -- (an establishment consisting of a building or complex of buildings where an organization for the promotion of some cause is situated)
3. (1) institution -- (a custom that for a long time has been an important feature of some group or society; "the institution of marriage"; "the institution of slavery"; "he had become an institution in the theater")
4. (1) initiation, founding, foundation, institution, origination, creation, innovation, introduction, instauration -- (the act of starting something for the first time; introducing something new; "she looked forward to her initiation as an adult"; "the foundation of a new scientific society"; "he regards the fork as a modern introduction")
5. mental hospital, psychiatric hospital, mental institution, institution, mental home, insane asylum, asylum -- (a hospital for mentally incompetent or unbalanced person)