(slang) A term of address, usually for a man, conveying awe, excitement, surprise, annoyance, etc.

To address someone as dude. / To take a vacation in a dude ranch. / (US) Usually followed by up: to dress up, to wear smart or special clothes.

(idiomatic) A young person who is ugly, but who is expected to become beautiful as they mature.

(of a statement, matter, or thing) Arousing doubt; questionable; open to suspicion. / (of a person) In disbelief; wavering, uncertain, or hesitating in opinion; inclined to doubt; undecided.

A fictional anthropomorphic black duck in the Looney Tunes and Merrie Melodies series of animated cartoons by Warner Bros.

(usually used attributively) A duck, comical especially for lisping voice or zany behavior.

One of the Disney cartoon characters, an anthropomorphic white-feathered duck who usually wears a sailor suit and is known for his voice especially in tantrums. / The asteroid 12410.

(Cockney rhyming slang) A fuck.

A classification into two subclasses or opposed parts. / (projective geometry) The interchangeability of points and planes.

(physics) The concept applying to all matter and radiation, but most evident in light and particles such as the electron, that properties of waves and of particles are exhibited simultaneously