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
any of several small freshwater European fishes of the genus Cottus, esp C. gobio, having a flattened body: family Cottidae (bullheads, etc)
Word Origin for miller's thumb
C15: from the alleged likeness of the fish's head to a thumb
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012