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"scrawl aimlessly," 1935, from dialectal doodle, dudle "fritter away time, trifle," or associated with dawdle. It was a noun meaning "simple fellow" from 1620s.
LONGFELLOW: That's a name we made up back home for people who make foolish designs on paper when they're thinking. It's called doodling. Almost everybody's a doodler. Did you ever see a scratch pad in a telephone booth? People draw the most idiotic pictures when they're thinking. Dr. Von Holler, here, could probably think up a long name for it, because he doodles all the time. ["Mr. Deeds Goes to Town," screenplay by Robert Riskin, 1936; based on "Opera Hat," serialized in "American Magazine" beginning May 1935, by Clarence Aldington Kelland]Related: Doodled; Doodling.
Doodle Sack. A bagpipe. Dutch. -- Also the private parts of a woman. ["Classical Dictionary of the Vulgar Tongue," 1796]
[second sense apparently coined by Robert Riskin, screenwriter for the movie Mr Deeds Goes to Town; third sense perhaps fr doo, childish word for ''shit'']
absent-minded scrawl or scribble, usually executed in some unexpected place, such as the margin of a book or manuscript or a blotting pad when the doodler is preoccupied with some other activity, such as attending a meeting or lecture. The word is supposed to have gained currency because of its use in the film Mr. Deeds Goes to Town (1936), though the practice of course is much older, doodles being found in medieval manuscripts, as well as in the notebooks of Leonardo da Vinci and on the margins of manuscripts written by Fyodor Dostoyevsky.