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.-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.