Dude! Where does the word dude come from?

with thanks to Taking English One Thumb at a Time
(dūd, dyūdpronunciation
  1. Informal. An Easterner or city person who vacations on a ranch in the West.
  2. Informal. A man who is very fancy or sharp in dress and demeanor.
  3. Slang.
    1. A man; a fellow.
    2. dudes Persons of either sex.
Slang. To dress elaborately or flamboyantly: got all duded up for the show.

interj. Slang
Used to express approval, satisfaction, or congratulations. Source

The origins of the word dude are disputed but certainly date back a little further than Dude, Where’s my Car? (2000). According to the American Heritage Dictionary: 
Originally it was applied to fancy-dressed city folk who went out west on vacation. In this usage it first appears in the 1870s.

A New York newspaper declared one Evan Berry (left) the ‘King of the Dudes’ in 1888. 'Dude' makes an appearance  in Mark Twain’s A Connecticut Yankee in King Arthur’s Court (1889) and pops up in the letters of an unlikely hipster P.G Woodhouse the only English characters the American public would read about were exaggerated dudes. 
In the 1962 John Ford western, The Man who Shot Liberty Valance the eponymous berates Ranse Stoddard (James Stewart) as a 'dude' - a Fancy-Dan lawyer and interloper. 

At the same time, dude was gaining a new lease of life; first as surfer slang and then more generally amongst west-coast hipsters. It appears in the uber-cool counter-cultural film Easy Rider (1969), though the Peter Fonda character has to have its meaning explained to him.  

True to form, David Bowie boldly injected the word into popular culture All the Young Dudes (1972) , while  Steely Dan followed with Every Major Dude (1974). 

Outside of California dude faded in the same way as ‘groovy’ and ‘gear’ went out of fashion. For next generation hipsters the word was slightly embarrassing reminder of the 60s. 

Gradually dude regained its kudos, though until the early 1990s dude was a word largely confined to Californians, cool teens, surfers and aspiring hipsters. 

It was the success of The Big Lewbowski (1998) which turned 'dude' from the linguistic equivalent of a cult Indie band to the U2 of contemporary vocabulary - even spawning a 'religion, Dudeism - see here.

Now dude is everywhere, dude. It has a wide range of uses (including use as an all-purpose interjection for expressing approval: "Dude!")

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