isinglass

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A transparent, almost pure gelatin prepared from the air bladder of the sturgeon and certain other fishes and used as an adhesive and a clarifying agent.
2. n. Mica in thin, transparent sheets.

Century Dictionary and Cyclopedia

1. n. The purest commercial form of gelatin, a substance of firm texture and whitish color, prepared from the sounds or air-bladders of certain fresh-water fishes. Isinglass is manufactured especially from the sounds of some species of Russian sturgeon, and in the United States from the sounds of cod, hake, squeteague, sea-trout, sturgeon, and other fishes, and from the skins of some of them. An inferior quality is made from clean scraps of hide, etc., or from the purified jelly obtained from skins, hoofs, horns, etc. In the preparation of creams and jellies isinglass is in great request. It is also used in fining liquors of the fermented kind, in purifying coffee, in making mock pearls, and in stiffening linens, silks, gauzes, etc. With brandy it forms a cement for mending broken porcelain and glass. It is likewise used as an agglutinant to glue together the parts of musical instruments, and for binding many other delicate fabrics. It is used in the manufacture of fine glues and sizes, adhesive plasters, court-plasters, diamond cement, and imitation glass, in refining wines and liquors, in adulterating milk, and in lustering silk ribbons. Grades are known as lyre, leaf, and book isinglass. In the East Indies, China, and Japan, isinglass, or its equivalent, is prepared from various algæ or seaweeds—the same in part which furnish the material of the bird's-nests prized as a delicacy by the Chinese. Such is the origin of the important Bengal isinglass or agar-agar. Japanese isinglass is afforded by species of Gelidium, and is said to produce a firmer jelly than any other gelatin. These various products are used not only for food, but in the arts for stiffening, varnishing, and gluing.
2. n. Mica: so called from its resemblance to some forms of the gelatin.

Wiktionary

1. n. A form of gelatine obtained from the air bladder of the sturgeon and certain other fish, used as an adhesive and as a clarifying agent for wine and beer.
2. n. A thin, transparent sheet of mica.

GNU Webster's 1913

1. n. A semitransparent, whitish, and very pure form of gelatin, chiefly prepared from the sounds or air bladders of various species of sturgeons (as the Acipenser huso) found in the rivers of Western Russia. It used for making jellies, as a clarifier, etc. Cheaper forms of gelatin are not unfrequently so called. Called also fish glue.
2. n. (Min.) A popular name for mica, especially when in thin sheets.

WordNet 3.0

1. n. any of various minerals consisting of hydrous silicates of aluminum or potassium etc. that crystallize in forms that allow perfect cleavage into very thin leaves; used as dielectrics because of their resistance to electricity