means Tangled and pressed into a dense, knotted mass, as hair, fur, or fibers become when they clump together and lose their separate strands.

from From 'mat,' the word for a rough woven floor-covering, which traces back through Old English 'matte' to Late Latin 'matta' — a covering of woven rushes or reeds. To be 'matted,' then, is to take on the character of that humble plaited mat: strands crossing, locking, fusing into one tangled fabric. The textile sense of 'matte' (dull, flat) is a separate cousin from French.