noun, noun which may take the genitive case particle 'no'
officially licensed; chartered; legitimate
A yojijukugo meaning something is officially permitted or recognized by the highest authority (originally the shogunate). Often used with a sense of being openly acknowledged or beyond reproach.
彼は天下御免の酒好きだ。
He is a self-proclaimed (and openly acknowledged) lover of sake.
この店は天下御免の老舗だ。
This shop is a long-established, officially recognized business.
公認 is a more neutral, modern term for official recognition, while 天下御免 carries a historical, somewhat grandiose nuance of being sanctioned by the highest authority.
Literally 'imperial pardon' or 'permission of the realm'. Originally referred to something officially permitted by the shogunate or central government. Now used idiomatically to mean something is openly acknowledged or beyond question.