byssus

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. Zoology A mass of strong, silky filaments by which certain bivalve mollusks, such as mussels, attach themselves to rocks and other fixed surfaces.
2. n. A fine-textured linen of ancient times, used by the Egyptians for wrapping mummies.

Century Dictionary and Cyclopedia

1. n. Among the ancients, originally, a fine yellowish flax, especially Indian and Egyptian, and the linen made from it, such as the Egyptian mummy-cloth; afterward, also, cotton and silk (the latter, before its origin was known, being taken for a kind of cotton).
2. n. One of the byssi, a name formerly given by botanists to a heterogeneous collection of filamentous cryptogamic plants.
3. n. In conchology, a long, delicate, lustrous, and silky bunch of filaments, secreted by the foot, and serving as a means of attachment to other Objects. It is developed in various dissimilar bivalve mollusks, especially by species of the families Mytilidæ, Pinnidæ, Aviculidæ, Limidæ, Arcidæ, Tridacnidæ, etc. That of the Pinna is capable of being woven. See Pinna, and also cuts under Dreissenidæ and Tridacnidæ.

Wiktionary

1. n. An exceptionally fine and valuable fibre or cloth of ancient times. Originally used for fine flax and linens, its use was later extended to fine cottons, silks, and sea silk.
2. n. The long fine silky filaments excreted by several mollusks (particularly Pinna nobilis) by which they attach themselves to the sea bed, from which sea silk is manufactured.
3. n. The stipe or stem of some fungi which are particularly thin and thread-like.

GNU Webster's 1913

1. n. A cloth of exceedingly fine texture, used by the ancients. It is disputed whether it was of cotton, linen, or silk.
2. n. (Zoöl.) 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. n. (Bot.) An obsolete name for certain fungi composed of slender threads.
4. n. Asbestus.

WordNet 3.0

1. n. tuft of strong filaments by which e.g. a mussel makes itself fast to a fixed surface