Way back in the 14th century, before the Industrial Revolution, woolen goods were milled by hand, on looms of limited width, capable of holding only a limited length of woven fabric. It’s still done this way by handcrafters.
The hand shuttle’s product wasn’t finished until it had been fulled (which, of course, is where the surname Fuller came from), using fuller’s earth, a type of clay. Notice that they weren’t making felt, here, or boiled wool—just the usual woolen goods that would be cut and sewn into, oh, Harris tweed and such.
Well, how do you dry a considerable length of washed wool? On a frame (a “tenter”), of course, stretched by its selvedges across hooks.
On particularly productive days, whole fields would bloom with tenters set out in the sun. It must have been quite a sight.
In miniature, we do pretty much the same thing when we block a finished piece of knitting, pinning it to shape on a cardboard cutting board. Steaming it lightly or thoroughly. Letting it dry before removing the pins.
The tenterhooks are still with us.