grayling \gray"ling\, n. from gray, a.
   1. zool. 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.
      1913 webster

            and here and there a lusty trout,
            and here and there a grayling.        --tennyson.
      1913 webster

   2. zool. 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.
      1913 webster
see also:
gray thymallus vulgaris umber thymallus t. ontariensis t. montanus