miller's-thumb

[ mil-erz-thuhm ]
/ ˈmɪl ərzˈθʌm /

noun

any of several small, freshwater sculpins of the genus Cottus, of Europe and North America.

Origin of miller's-thumb

1400–50; late Middle English milneres thume; the fish is so called from its thumblike head
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019