When the feet wore out on socks and stockings, they would unravel them, save the good thread, and reknit the foot or toe or heel.
Old English cnyttan "to tie with a knot, bind, fasten," related to Old Norse knytja "bind together," Middle Low German knütten "to tie, knot," Old English cnotta "a knot," from Proto-Germanic *knuttjan, from stem *knutt-. Of brows, late 14c. Meaning "to do knitting" (especially plain stitch) is from 1520s. Related: Knitted; knitting.