English:
* Booklet: A small book, often with a paper cover.
* Libretto: A booklet containing the words of an opera or musical.
* Pamphlet: A small book with a paper cover, usually dealing with a specific topic.
Other languages:
* French: Livret (small book)
* Spanish: Librito (small book)
* Italian: Libretto (small book)
* German: Büchlein (small book)
There isn't one single, universally accepted diminutive for "book" in English. The most common and widely understood diminutive is booklet.