Definitions of Palimpsest according to OED

palimpsest n. and a.
1. Paper, parchment, or other writing-material prepared for writing on and wiping out again, like a slate.
1661 Lovell Hist. Anim. & Min. 7 The chalked skinne for a palimpsestus, serving in stead of a table book.
1662 Evelyn Chalcogr. (1769) 52 In writing, the use of the palimpsestus..and the like.
1706 Phillips, Palimpseston,..a sort of Paper or Parchment, that was generally us’d for making the first draught of things, which might be wip’d out, and new wrote in the same Place.
2. A parchment or other writing-material written upon twice, the original writing having been erased or rubbed out to make place for the second; a manuscript in which a later writing is written over an effaced earlier writing.
1825 Gentl. Mag. XCV. i. 348 Monsignore Angelo Mayo..celebrated for his discoveries in the ‘Palimpsestes’.
1838 Arnold Hist. Rome I. 256 note, The Institutes of Gaius..was first a palimpsest, or rewritten manuscript of S. Jerome, in the Chapter Library at Verona.
1875 Scrivener Text N. Test. 18 To decipher a double palimpsest calls for the masterhood of a Tischendorf.
1845 De Quincey Suspiria Wks. 1890 XIII. 346 What else than a natural and mighty palimpsest is the human brain?
1856 Mrs. Browning Aur. Leigh i. 826 Let who says ‘The soul’s a clean white paper’ rather say A palimpsest..defiled.
1879 Lewes Study Psychol. viii. 153 History unrolls the palimpsest of mental evolution.
1918 D. H. Lawrence New Poems 33 Darkness comes out of the earth..Wanes the old palimpsest.
1929 Oxford Poetry 17 The world is all a palimpsest That hails the spurious pugilist.
1949 ‘G. Orwell’ Nineteen Eighty-Four i. iv. 42 All history was a palimpsest, scraped clean and re-inscribed exactly as often as was necessary.
1962 R. Page Educ. Gardener x. 294 In Italy every town and a palimpsest of two or three thousand years of building and decay.

De Quincey, Thomas

"The Palimpsest of the Human Brain" Suspiria de Profundis. Edinburgh: Adam and Charles Black, 1871. 10-22.

". . . A palimpsest, then, is a membrane or roll cleansed of its manuscript by reiterated successions. [. . .] What else than a natural and mighty palimpsest is the human brain? Such a palimpsest is my brain; such a palimpsest, oh reader! is yours. Everlasting layers of ideas, images, feelings, have fallen upon your brain softly as light. Each succession has seemed to bury all that went before. And yet, in reality, not one has been extinguished. And if, in the vellum palimpsest, lying amongst the other diplomata of human archives or libraries, there is any fantasticor which moves to laughter, as oftentimes there is in the grostesque collisions of those successive themes, having no natural connection, which by pure accident have consecutively occupied the roll, yet, in our own heaven-created palimpsest, the deep memorial palimpsest of the brain, there are not and cannot be such incoherencies. The fleeting accidents of a man’s life, and tis external shows, may indeed be irrelate and incongruous; but the organising principles which fuse into harmony, and gather about fixed predetermined centres, whatever heterogeneous elements life may have accumulated from without, will not permit the grandeur of human unity greatly to be violated, or its ultimate repose to be troubles, in the retrospect from dying moments, or from other great convulsions.[ . . .]