You may need to consume another module from your definition file. The reason might be to get types from another library. To be able to use the type of another library, you can use import * and assign an alias with as from the type you want to refer in your definition file:

declare module "react-summernote" {
  import * as React from "react";
  let ReactSummernote: React.ComponentClass<any>;
  export default ReactSummernote;
}