miller'sthumb

mill·er's thumb (mĭlʹərz) n.

Any of several small freshwater sculpins of the genus Cottus, especially C. gobio, found in Europe and North America and having a large spiny head and spiny fins.

  [From its stocky, thumblike shape (the phrase miller's thumb was originally a folk expression referring to millers who gave short weight by tipping the scales with their thumbs).]

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