It's not what you're thinking. I'm using the word in the sense of its second, slightly less derogatory meaning:
(adjective) demonstrating or implying an undiscriminating or unselective approach; indiscriminate or casual.
"the city fathers were promiscuous with their honors"
synonyms: indiscriminate, undiscriminating, unselective, random, haphazard, irresponsible, unthinking, unconsidered
From page 26:
This idea came to mind when I started reading my latest eBay acquisition: a set of books called "The Golden Treasury of Knowledge" Margaret Bevans, editor-in-chief. The 16-volume set, originally published by Golden Press in 1961, contains "420 basic articles with 2500 illustrations and maps; not organized alphabetically—random articles on a wide range of topics in each volume, cross-referenced in the index (vol 16). Intended for children (level probably around age 8-12)." This description comes from Goodreads.
When I was young, our family had a set of encyclopedias, but this is something different. The introduction in Volume 1 states, "The articles in the volume are chosen for variety and interest. You can open the book anywhere and find absorbing reading. But when you have read an article that suggests another idea, look in the index in Volume 16 for related articles and facts." What I like about this method is that it is both thought-out and systematic while appealing to the random "scrappy" impulses of a curious mind.
Now, for a sample of the promiscuous content of Volume 1: The Universe, Giotto, Domestic Cats, The First Firearms, Venezuela, The Chestnut Blight, Molecules and Their Structure, The French Revolution. At the back of each volume there is a time chart showing how the periods of history relate and at what time the events in the articles took place.
These are the kinds of books for whiling away an afternoon, whether you are nine years old or a little bit older. And please don't tell me that all this information is available online. While that's perfectly true, it doesn't suit me to stare at a screen any longer than I already do. These books are refreshing, in an old-school kind of way.