Completely healed or cured, as in Once we've bandaged it up, you'll be all better. This term is often used to comfort a child who has been hurt. It uses all in the sense of "entirely" and better in the sense of "cured.". The usage has been in the language since a.d. 1000.
Dictionary.com presents 366 FAQs, incorporating some of the frequently asked questions from the past with newer queries.