From WordNet (r) 3.0 (2006) [wn]:
dude
n 1: an informal form of address for a man; "Say, fellow, what
are you doing?"; "Hey buster, what's up?" [syn: fellow,
dude, buster]
2: a man who is much concerned with his dress and appearance
[syn: dandy, dude, fop, gallant, sheik, beau,
swell, fashion plate, clotheshorse]
From The Collaborative International Dictionary of English v.0.48 [gcide]:
Dude \Dude\, n.
A kind of dandy; especially, one characterized by an
ultrafashionable style of dress and other affectations.
[Recent]
[1913 Webster]
The social dude who affects English dress and English
drawl. --The
American.
[1913 Webster]