1766, in a British sense, "class of people socially intermediate between the aristocratic and the laboring classes, the community of untitled but well-bred or wealthy people," from middle (adj.) + class (n.). As an adjective, "pertaining to the middle class," by 1857, with reference to education. Nares reports menalty as an early word for "the middle class" (1540s).
1722, originally nautical, also close-fights, "bulkheads fore and aft for men to stand behind in close engagements to fire on the enemy," it reflects the confusion of close (v.) and close (adj.); "now understood of proximity, but orig. 'closed' space on ship-board where last stand could be made against boarders" [Weekley]. Compare also closed-minded (1880s), a variant of close-minded, as if "shut" rather than "tight," also closed-fisted, occasional variant of close-fisted "stingy."
"closed end of a passage," 1851 in reference to drainpipes, 1874 in reference to railway lines; by 1886 of streets; from dead (adj.) + end (n.). Figurative use, "course of action that leads nowhere," is by 1914. As an adjective in the figurative sense by 1917; as a verb by 1921. Related: Dead-ended; dead-ending; deadender (by 1996).