Etymology
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cobra (n.)

venomous hooded snake found in India and neighboring regions, 1802, short for cobra capello (1670s), from Portuguese cobra de capello, literally "serpent of the hood," from Latin colubra "a snake, female serpent" (source of French couleuvre "adder"), which is of uncertain origin. So called for the expandable loose skin about its neck. The word came to English via Portuguese colonies in India, where the native name is nag (see naga).

De Vaan suggests a possible connection of Latin colubra with colus "distaff." "A distaff is used to wind a thread or fibre around it. Hence, a preform *kolos-ro- would mean 'distaff-like' or 'of a distaff' ..., and since a snake also winds around its own axis, it might have been called 'distaff-like animal'."

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king (adj.)

king (n.) applied, at first in natural history, to species deemed remarkably big or dominant, such as king crab (1690s); the U.S. king snake (1737), which attacks other snakes and is regarded especially as the enemy of the rattlesnake; king cobra (1888). In marketing, king-size is from 1939, originally of cigarettes. A king-bolt (1825) was the large bolt connecting the fore part of a carriage with the fore-axle.

The King-snake is the longest of all other Snakes in these parts, but are not common; the Indians make Girdles and Sashes of their Skins, and it is reported by them, that they are not very venemous, and that no other Snake will meddle with them, which I suppose is the Reason that they are so fond of wearing their Skins about their Bodies as they do. [John Brickell, "The Natural History of North-Carolina," Dublin, 1737]
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