Where did this term originate, and how? Aren't most of them pure propaganda mills? Indeed, are there any that aren't?

According to Wikipedia,

quote:

The phrase "think tank" in wartime American slang referred to rooms in which strategists discussed war planning.

This page gives more details.

It's interesting how times change. About 8 or so years ago, in my field "think tanks" were all the rage in nursing. Now the terminology has evolved to though leaders or maybe expert or blue ribbon panels.