c. 1300, devis, "intent, desire; an expressed intent or desire; a plan or design; a literary composition," from Old French devis "division, separation; disposition, wish, desire; coat of arms, emblem; a bequest in a will, act of bequeathing," from deviser "arrange, plan, contrive," literally "dispose in portions," from Vulgar Latin *divisare, frequentative of Latin dividere "to divide" (see divide (v.)).
The basic sense is "method by which something is divided," which arose in Old French and led to the range of modern meanings via the notion of "something invented or fitted to a particular use or purpose," hence "an invention; a constructed tool; inventiveness; a contriving, a plan or scheme."
In English from c. 1400 as "artistic design, work of art; ornament," hence especially "a representation of some object or scene, accompanied by a motto or legend, used as an expression of the bearer's aspirations or principles." Also from c. 1400 as "mechanical contrivance," such as a large crossbow fitted with a crank. From mid-15c. as "a bequest in a will." Since c. 1996 the word has come to be used especially for "hand-held or mobile computing or electronic instrument."
We live in a kind of world and in an age of the world where devices of all sorts are growing in complexity, where, therefore, the necessity for alertness and self-mastery in the control of device is ever more urgent. If we are democrats we know that especial perils beset us, both because of the confusion of our aims and because it is easier for the mob than for the individual to mistake appetite for reason, and advantage for right. [Hartley Burr Alexander, "'Liberty and Democracy,' and Other Essays in War-Time," 1918]