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book gill

American  

noun

  1. the gill of a horseshoe crab, composed of numerous membranous structures arranged like the leaves of a closed book.

Etymology

Origin of book gill

First recorded in 1895–1900

Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.