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).
It is clear that none of the unfortunate people, perhaps at this moment on board, can stand upright, but that they must sit down, and contract their limbs within the limits of little more than three square feet, during the whole of the middle passage. I cannot compare the scene on board this vessel, to any other than that of a pen of sheep; with this difference only, that the one have the advantages of a wholesome air, while that, which the others breathe, is putrid. [Thomas Clarkson, "An Essay on the Slavery and Commerce of the Human Species," 1788]
"period between ancient and modern times" (formerly roughly 500-1500 C.E., now more usually 1000-1500), attested from 1610s, translating Latin medium aevum (compare German mittelalter, French moyen âge).
1899; never defined in a generally accepted way. Early use with reference to British India; later often of everything between Egypt and Iran. Hence Middle-Eastern (1903).
"Middle East," attested from 1944 in reference to western Asia. Loosely defined (compare Middle East).
"Pole Star, Polaris," Middle English norþe sterre (late 14c.); cognate with Middle Dutch noirdstern, German Nordstern.
"nakedness," 1730s, but probably much older. The notion is the suit of clothes one was born in, i.e., no clothes at all. Compare Middle English mother naked "naked as the day one was born;" Middle Dutch moeder naect, German mutternackt.