early 15c., "fur or pelt of the European sable" (Martes zibellina), from Old French sable (also martre sable "sable martin"), in reference to the carnivorous arctic mammal or its highly prized fur, borrowed in French from Germanic (compare Middle Dutch sabel, Middle Low German sabel, Middle High German zobel), ultimately from a Slavic source (compare Russian, Czech sobol, Polish soból, the name of the animal), "which itself is borrowed from an East-Asiatic language" [Klein], but Russian sources (such as Vasmer) find none of the proposed candidates satisfactory.
In reference to the animal itself in English from mid-15c. The earlier word for the fur was sabeline (c. 1200), from Old French sabeline and directly from Medieval Latin sabelinum.
early 14c., "black" as a heraldic color, commonly identified with sable (n.1) and in many dictionaries they form one entry, but the animal's fur is brown (though generally darker than the fur of other animals) and this might be a different word of unknown origin, or it might reflect a medieval custom (unattested) of dyeing sable black. As an adjective from late 14c. Emblematic of mourning or grief from late 14c.; by c. 1800 as "black" with reference to Africans and their descendants, often in mock dignity.