isinglass

n. [ Prob. corrupted fr. D. huizenblas (akin to G. hausenblase), lit., bladder of the huso, or large sturgeon; huizen sturgeon + blas bladder. Cf. Bladder, Blast a gust of wind. ] [ 1913 Webster ]

1. 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. [ 1913 Webster ]

2. (Min.) A popular name for mica, especially when in thin sheets. [ 1913 Webster ]