You mean libel. Slander is spoken, libel is written.
The easy way to remember this distinction is to know that one of the most famous libel cases in history, nicknamed the "McLibel" case, concerned printed pamphlets.
Hm, I can't edit my comment anymore, but French wiktionary claims that French "livre" (meaning pound) comes from the Latin word for the measure that weighed about as much as a book. ("livre" also means "book" in French).
I guess "lb." and French "livre" (meaning pound) aren't necessarily related. More likely: wiktionary could be full of shit, meaning I was wrong.