minnow

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

• noun Any of a large group of small freshwater fishes of the family Cyprinidae, widely used as live bait.
• noun Any of various other small, often silver-colored fishes.

from The Century Dictionary.

• noun A name sometimes given to a very small fish of New Zealand, Galaxias attenuatus, of the family Galaxidæ. Also called whitebait. The Maori name is inanga.
• noun See leatherside.
• noun The smallest of the British cyprinoid fishes, Phoxinus aphya or lævis.
• noun In the United States, one of many different fishes of small size,

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

• noun (Zoöl.) A small European fresh-water cyprinoid fish (Phoxinus lævis, formerly Leuciscus phoxinus); sometimes applied also to the young of larger kinds; -- called also minim and minny. The name is also applied to several allied American species, of the genera Phoxinus, Notropis, or Minnilus, and Rhinichthys.
• noun (Zoöl.) Any of numerous small American cyprinodont fishes of the genus Fundulus, and related genera. They live both in fresh and in salt water. Called also killifish, minny, and mummichog.

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

• noun A small freshwater fish of the carp family.
• noun More generally, any small fish.
• noun soccer A low-level team, in comparison to their opponents.
• verb fishing to fish minnows
• verb fishing to fish (especially trout) using a minnow as bait

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun very small European freshwater fish common in gravelly streams