\Bys"sus\, n.; pl. E. {Byssuses}; L. {Byssi}.[L. byssus
fine flax, fine linen or cotton, Gr. by`ssos .]
1. A cloth of exceedingly fine texture, used by the ancients.
   It is disputed whether it was of cotton, linen, or silk.
   [Written also {byss} and {byssin}.]

2. (Zo["o]l.) 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.

3. (Bot.) An obsolete name for certain fungi composed of
   slender threads.

4. Asbestus.