Why is the "Dutch" roll called so? When did this name enter common usage, and what is its origin? Please cite sources if possible!
According to Wikipedia:
"The origin of the name Dutch roll is uncertain. However, it is likely that this term, describing a lateral asymmetric motion of an airplane, was borrowed from a reference to similar-appearing motion in ice skating. In 1916, aeronautical engineer Jerome C. Hunsaker published the following quote: "Dutch roll – the third element in the [lateral] motion [of an airplane] is a yawing to the right and left, combined with rolling. The motion is oscillatory of period for 7 to 12 seconds, which may or may not be damped. The analogy to 'Dutch Roll' or 'Outer Edge' in ice skating is obvious." In 1916, Dutch Roll was the term used for skating repetitively to right and left (by analogy to the motion described for the aircraft) on the outer edge of one's skates. By 1916, the term had been imported from skating to aeronautical engineering, perhaps by Hunsaker himself. 1916 was only five years after G. H. Bryan did the first mathematics of lateral motion of aircraft in 1911."
Sadly, this question is probably not answerable beyond what wikipedia has on this site (unless there is an English Major looking for a Ph.D. thesis. ;)
An early use of "Dutch rolls" in aeroplaning is 1910:
Fancy aeroplaning was on the programme at the Harvard Aviation Field the next day, with Ralph Johnstone and Walter Brookins as the star performers. They demonstrated their skill with the biplanes until Wilbur Wright feared for their safety and ordered them to desist. Johnstone's favorite stunt was to indulge in steep volplanes, shutting his engine almost completely off and floating lazily for a moment on an even keel, then suddenly shooting down through space until het almost touched the ground. Then would follow a series of Dutch rolls as he swooped up and down close to earth.
Conquest of the Air by Airships and Other Flying Machines, Jay Henry Mowbray, 1910. (Link)
In Dutch, this motion is called zwierbeweging: swaying motion. Indeed the motion that can be observed during ice skating on modern metal skates.
I unfortunately have no official reference other than videos of for instance this event. Swaying Dutch roll everywhere.