noun asbestus.
2. byssus ·noun an obsolete name for certain fungi composed of slender threads.
3. byssus ·noun a cloth of exceedingly fine texture, used by the ancients. it is disputed whether it was of cotton, linen, or silk.
4. byssus ·noun a tuft of long, tough filaments which are formed in a groove of the foot, and issue from between the valves of certain bivalve mollusks, as the pinna and mytilus, by which they attach themselves to rocks, ·etc.