Green’s Dictionary of Slang

dude n.1

also dood
[duds n.1 (1) or abbr. SE attitude. The term gained a whole new currency, esp. among the pre-teens, with the popularity c.1990 of the cartoon characters Teenage Mutant Ninja Turtles, where it featured heavily; note also in Comments on Etymology Apr. 1997, Gerald Cohen has posited an orig. pron. of doo-dee and suggested an origin in Yankee Doodle + SE dandy]

1. [late 19C+] (orig. US, also dudelet) a man, a fellow; post 1980s, a person, irrespective of gender.

2. [late 19C+] (orig. US) an overdressed, showy person, a fop or dandy.

3. [late 19C] (Aus.) a womanizer.

4. [1900s] (US campus) a fool.

5. [1910s] (US) an expert.

6. [1920s] an excellent example.

7. [1950s+] (US) a thing.

8. [1960s+] a form of address.

In derivatives

dudelet (n.)

see sense 1 above.

dudester (n.) [-ster sfx]

[1980s] (US) a person, irrespective of gender.

dudette (n.) (also dudess, dudine, dudinette) [fem. sfx -ette]

[late 19C+] (US) a girl, a woman; often with a suggestion of stylishness or ostentation.

dudish (adj.) (also doodish, dudeish)

[late 19C+] smart, dandyish.

dudeism (n.)

affectation.

In phrases

big dude (n.)

[1960s] (US) an important person.

dude up (v.)

[20C+] (US) to dress (oneself) up.