A relatively large silversides of the Pacific coast of North America (known to reach 18 inches in length)(noun)
WordNet. Princeton University. 2010.
Use "jacksmelt" in a sentence
"The report specifically identifies jacksmelt and Pacific chub mackerel as being safe to eat multiple times per week in small portions of 3ounces each."
"My dad told me about the jacksmelt, a fish so dumb that you catch them without even baiting the hook."