roller n.

early 14c., rollen, "turn over and over, move by rotating" (intransitive); late 14c. in the transitive sense of "move (something) by turning it over and over;" from Old French roeller "roll, wheel round" (Modern French rouler), from Medieval Latin rotulare, from Latin rotula, diminutive of rota "wheel" (see rotary). Related: Rolled; rolling.

From c. 1400 as "wrap or cover by rolling or enclosing" in something, also "wrap round and round an axis;" early 15c. as "press or level with a roller." From 1510s as "to move or travel on wheels or by means of rolling." Of sounds (such as thunder) somehow suggestive of a rolling ball, 1590s; of a drum from 1680s.

Of spoken sounds, "to utter with vibrations of the tongue," by 1846. Of eyes, from late 14c. (rolle his eyne), originally suggestive of ferocity or madness. Of a movie camera, "to start filming," from 1938. Sense of "rob a stuporous drunk" is by 1873, from the action required to get to his pockets. To roll up "gather, congregate" is from 1861, originally Australian. To roll with the punches is a metaphor from boxing (1940). To roll them bones was old slang for "play at dice" (1929). Heads will roll is a Hitlerism:

If our movement is victorious there will be a revolutionary tribunal which will punish the crimes of November 1918. Then decapitated heads will roll in the sand. [1930]

town and county in England, Old English Deorby "deer village," from deor "deer" (see deer) + by "habitation, homestead," from a Scandinavian source (see first element in bylaw). the annual Derby horse race, the most important in England, was begun 1780 by the 12th Earl of Derby and run at Epsom, Surrey; the name was used for any major horse race after 1875. Hence Derby day (generally the Wednesday before Whitsuntide), etc.

Derby dog, something that "turns up" without fail, as the proverbial dog on the race-course on Derby day, after the track is otherwise cleared for the races. [Century Dictionary; the phrase is attested from 1858] 

The type of stiff, felt hat with a rounded crown and more or less narrow brim was manufactured in U.S. by 1850 and called by that name by 1870; perhaps so called because it was worn in riding. It came in as a fashionable novelty in 1874.