I looked up the word with Merriam-Webster (a dictionary website that I will use while I'm online) and found several definitions for the word 'cowl.' The best fit for the definition was "a draped neckline on a woman's garment." Didn't seem to quite fit, because these warm cowls aren't really just on the neckline nor just for women. So, I saw there was a definition option for 'cowl-neck' defined as "a high loose-fitting turnover collar used especially for sweaters." Ha! This seems quite a bit better definition. Come to think of it, these cowls that have become so popular really are like detached collars of a sweater. I guess that's where the name came from. :p
Anyway, I have been tinkering with my own designs for cowls. The picture above is one of the two I've made so far. They're actually quite easy. There are a couple options you have when making a cowl. You can make a large rectangle, long enough to go around your neck and wide enough to cover it, and whip stitch it together or use button fasteners like I did. The second option is to knit or crochet in a round, again making sure you make it large enough to fit. Use whatever style of stitch you like! I mix and match mine for neat texture changes.