The Collaborative International Dictionary of English v.0.48:
Chub \Chub\, n. [This word seems to signify a large or thick
fish. Cf. Sw. kubb a short and thick piece of wood, and perh.
F. chabot chub.] (Zool.)
A species to fresh-water fish of the Cyprinid[ae] or Carp
family. The common European species is Leuciscus cephalus;
the cheven. In America the name is applied to various fishes
of the same family, of the genera Semotilus, Squalius,
Ceratichthys, etc., and locally to several very different
fishes, as the tautog, black bass, etc.
Chub mackerel (Zool.), a species of mackerel (Scomber
colias) in some years found in abundance on the Atlantic
coast, but absent in others; -- called also bull
mackerel, thimble-eye, and big-eye mackerel.
Chub sucker (Zool.), a fresh-water fish of the United
States (Erimyzon sucetta); -- called also creekfish.