The word "mook" is a portmanteau of the words "magazine" and "book." I had long assumed, mistakenly, that it was one of those examples of wasei-eigo (Japan-made English terms), such as "open car" (a convertible) or "virgin road" (the aisle down which the bride walks at a wedding ceremony). But from online searches I learned the term apparently originated in Europe, making its first appearance in 1971 at a convention of the London-based International Federation of Periodical Publishers.