grayling

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Any of several freshwater salmonid fishes of the genus Thymallus of northern North America and Eurasia, having a small mouth and a large dorsal fin and valued as a food and game fish.

from The Century Dictionary.

• noun A fish of the family Salmonidæ and genus Thymallus.
• noun The dace.
• noun A common European butterfly, Hipparchia semele: so called from the gray under side of the wings.
• noun In Australia, Prototroctes muræna, of the family Hoplochitonidæ, a fish which remotely resembles the English grayling. Also called cucumber-fish, cucumber-mullet, fresh-water herring, and Yarra herring.
• noun An American agapetid butterfly, Cercyonis alope, which occurs in several well-marked varieties. See below.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Zoöl.) A European fish (Thymallus vulgaris), allied to the trout, but having a very broad dorsal fin; -- called also umber. It inhabits cold mountain streams, and is valued as a game fish.
• noun (Zoöl.) An American fish of the genus Thymallus, having similar habits to the above; one species (T. Ontariensis), inhabits several streams in Michigan; another (T. montanus), is found in the Yellowstone region.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun Any freshwater fish of the genus Thymallus or specifically Thymallus thymallus, of the salmon family, having a large dorsal fin.
• noun A species of butterfly, Hipparchia semele, of the family Nymphalidae.