fish louse

noun

: any of various small crustaceans (as the carp louse) parasitic on fishes

especially : any of various true copepods that are found on the skin or gills or in the mouth of fishes and that exhibit varying degrees of degeneration in the adult state due to their parasitic habits see lernaea

The Ultimate Dictionary Awaits

Expand your vocabulary and dive deeper into language with Merriam-Webster Unabridged.

1. Expanded definitions
2. Detailed etymologies
3. Advanced search tools
4. All ad-free

Discover what makes Merriam-Webster Unabridged the essential choice for true word lovers.

Start Your Free Trial Now