Boulevard
2 of the 7 encyclopedias on this shelf carry an entry for Boulevard. Both are reproduced below, so you can see where they agree and where they differ.
Aiton's Encyclopedia (1910)
boo'le-vard, a broad street or drive, presumably lined with trees. The term is French, corresponding to the English bulwark, a defensive wall or rampart. As the need and indeed the utility of walls passed away, the medieval cities of Europe leveled their defenses into fine driveways encircling the historical centers. These new streets retained the old name of boulevard, formerly applied to the wall. These boulevards are a delightful parklike feature of European cities and indicate, even to a stranger, the position of the old fortifications and ditches. Bologna, Nuremberg, Constance, and Chester are among the few old cities that retain the traditional walls. By degrees the term boulevard has been extended to any broad street, especially one bordered or adorned with grass plots and ornamental shade trees and shrubbery. 2026 Editor's Note: The entry's pleasant tree-lined drives had a harder purpose in Paris. When Baron Haussmann drove his great boulevards through the medieval city in the 1850s and 60s, the wide straight avenues were understood to serve artillery and troop movement as well as air and light — much harder to barricade than the twisting lanes they replaced. (Ed: BR 2026-06-04)
Collier's New Encyclopedia (1921)
a French word formerly applied to the ramparts of a fortified town, but when these were leveled, and the whole planted with trees and laid out as promenades, the name boulevard was still retained. Modern usage applies it also to many streets, which are broad and planted with trees, although they were not originally ramparts. The most famous boulevards are those of Paris.