Meaning

noun primitive long-bodied carnivorous freshwater fish with a very long dorsal fin; found in sluggish waters of North America

noun any of several small sharks

originFrom dog + fish. Compare Greek σκυλόψαρο (skylópsaro, “dogfish”), Latin canicula (“dogfish”, literally “little dog”), Italian pescecane (“dogfish”), French chien de mer (literally “dog of the sea”), German Meerhund (literally “seadog”) and Hundfisch (“dogfish”), and English seadog. For non-Indo-European cognates, see Maltese kelb il-baħar (literally “dog of the sea”) and Turkish köpek balığı…

Etymology from Wiktionary, CC BY-SA 3.0