byssus

plural byssi · plural byssuses

1. uncountableusuallyThe long fine silky filaments excreted by several mollusks (particularly Pinna nobilis) by which they attach themselves to the sea bed, and from which sea silk is manufactured.
2. uncountableusuallySea silk manufactured from these filaments.

   This peculiar material is called byssus, and it's a counterexample, sort of, to the claim that no commercial fibers come from mollusks. Byssus is the fiber made by clams and mussels to glue themselves to rocks underwater.

   2014, Theodore Gray, photography by Nick Mann, Molecules: The Elements and the Architecture of Everything, 2018 Paperback Edition, page 123

3. uncountableusuallybiologyThe stipe or stem of some fungi which are particularly thin and thread-like.