also proletariate, "the lowest and poorest class," 1853, from French prolétariat, from Latin proletarius (see proletarian). In political economics, "indigent wage-earners, , the class of wage-workers dependent on daily or casual employment" from 1856. The Englished form proletary was used 16c.-17c. in the older sense and revived in the modern sense by 1865. The Leninist phrase dictatorship of the proletariat is attested from 1918.
1707, "body of freemen in a French town," hence, "the French middle class," also extended to that of other countries, from French bourgeois, from Old French burgeis, borjois (12c.) "town dweller" (as distinct from "peasant"), from borc "town, village," from Frankish *burg "city" (from PIE root *bhergh- (2) "high," with derivatives referring to hills and hill-forts). Communist use for "the capitalist class generally" attested from 1886.
1680s, "foundation beam of a dam, railroad, house, or other structure," from mud + sill. The word entered U.S. political history in a figurative sense in a speech by James M. Hammond (1807-1864) of South Carolina, March 4, 1858, in the U.S. Senate, alluding to the necessary lowest class of society. In the speech he also took the ground that Northern white laborers were slaves in fact, if not in name. The term subsequently was embraced by Northern workers in the pre-Civil War sectional rivalry.
In all social systems there must be a class to do the menial duties, to perform the drudgery of life. This is a class requiring but a low order of intellect and but little skill. Its requisites are vigor, docility, fidelity. Such a class you must have, or you would not have that other class which leads progress, civilization, and refinement. It constitutes the very mud-sill of society and of political government; and you might as well attempt to build a house in the air as to build either the one or the other except on this mud-sill. [Hammond]
"melted, in a state of solution," c. 1300, from archaic strong past participle of Old English meltian, a class III strong verb (see melt (v.)).