This ranks as another of those words that surprised me!
I’ve long known that people used to call small portraits miniatures–but what I didn’t realize was that the “small” part wasn’t the root of the word.
In fact, the word miniature comes from the Latin miniare, which means “to paint red.” (Red being one of the primary colors used in illumination [illustration] of manuscripts.) Who knew?! So back in the day, when people were making books by hand, they would put small pictures onto the page and color them in, which they, therefore, called “miniatures.” So naturally, it was only a matter of time before it came to mean any “small picture.” And from there, it shifted to mean anything small!