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Middle English word meaning "conscience" (early 13c.), "reason, intellect" (c.1300), from in (adv.) + wit (n.). Not related to Old English inwit, which meant "deceit." Joyce's use in "Ulysses" (1922), which echoes the 14c. work "Ayenbite of Inwyt," is perhaps the best-known example of the modern use of the word as a conscious archaism.
Þese ben also þy fyve inwyttys: Wyl, Resoun, Mynd, Ymaginacioun, and Thoght [Wyclif, c.1380]
If ... such good old English words as inwit and wanhope should be rehabilitated (and they have been pushing up their heads for thirty years), we should gain a great deal. [Robert Bridges, 1922]