Webster's Revised Unabridged Dictionary · 1913

Beluga

Beluga (be*lū"gȧ) , noun

[Russ. bieluga a sort of large sturgeon, prop. white fish, from bieluii white. The whale is now commonly called bieluka in Russian.]

1.
(Zoology) A cetacean allied to the dolphins.

The northern beluga (Delphinapterus catodon) is the white whale and white fish of the whalers. It grows to be from twelve to eighteen feet long.

2.
the sturgeon (Huso huso) native to the Black Sea and Caspian Sea; -- also called hausen. It is valued for its roe, sold as caviar, and is also used for production of isinglass. See also sturgeon.
3.
the caviar obtained from the beluga{2}; -- also called beluga caviar. The caviar of the beluga is considered the finest sort, larger and of a taste superior to that obtained from other sturgeon. See also sturgeon and caviar.