From the second edition (1989):
palimpsest, n. and a.
(ˈpælɪmpsɛst) Also 7–8 in L. or Gr. form. [ad. L. palimpsēstus n., a. Gr. παλίµψηστος scraped again, παλίµψηστον a parchment whence writing has been erased, f. πάλιν again + ψηστός, from ψάω, ψῆν to rub smooth.]

A. n.

1. Paper, parchment, or other writing-material prepared for writing on and wiping out again, like a slate. Obs. [So It. palimsesto (Florio).]

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 discovered‥in a palimpsest, or rewritten manuscript of‥works 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.
fig. 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 house‥is a palimpsest of two or three thousand years of building and decay. 1977 Times 3 Sept. 9/1 Alan Watts will be principally remembered as the architect of that peculiar theological palimpsest which served as an ideology for the hippie generation: that odd blend of rural fundamentalism and eastern mysticism.

3. A monumental brass slab turned and re-engraved on the reverse side.

1876 Encycl. Brit. IV. 219/2 A large number of brasses in England are palimpsests, the back of an ancient brass having been engraved for the more recent memorial. 1877 L. Jewitt Half-hrs. among Eng. Antiq. 132 They were frequently laid down to other persons, or re-engraved on the other side, and hence called palimpsests.

B. adj.

1. (Applied to a manuscript) Written over again; of which the original writing has been erased and superseded by a later: see A. 2.

1852 H. Rogers Ecl. Faith (1853) 237 A friend who used to mourn over the thought of palimpsest manuscripts. 1875 Poste Gaius Pref. (ed. 2) 5 The codex is doubly palimpsest, i.e. there are three inscriptions on the parchment. 1898 R. Harris in Expositor Dec. 402 It is useless to apply reagents in search of palimpsest writing where the vellum has only been used once.
fig. 1873 W. Cory in Lett. & Jrnls. (1897) 308 The pretty song, rising one will never know how, from a palimpsest memory.

2. Of a monumental brass: see A. 3.

1843 Archæologia XXX. 124 Palimpsest brasses are also found at Berkhampstead. 1877 J. C. Cox Ch. of Derbysh. III. 241 This monument is a remarkable‥example of the palimpsest or re-used brass.

3. Petrogr. Of a rock: partially preserving the texture it had prior to metamorphism. Also in Geol., exhibiting features produced at two or more distinct periods.

1912 R. W. Clark tr. Weinschenk's Petrogr. Methods x. 198 In the normal case the newly developed substance is confined strictly to the border of the original crystal, but the texture of the altered rock may be recognized excellently, palimsest [sic] structure. 1926 G. W. Tyrrell Princ. Petrol. xvi. 271 (caption) A palimpsest structure. Garnetiferous biotite-hornfels.‥ Shows alternations of psammitic and pelitic sediments preserved, although the rock is thoroughly hornfelsed with the production of muscovite and biotite. 1951 Turner & Verhoogen Ign. & Metamorphic Petrol. xx. 503 It frequently happens‥that fabric relicts (palimpsest structures), like mineral relicts, survive metamorphism and provide valuable indications of the parentage of the metamorphic rock. 1962 A. D. Howard in Bull. Amer. Assoc. Petroleum Geologists XLVI. 2255/1 A particularly interesting part of the anomaly is the drainage pattern, an unusual superposition of modern and ancient patterns that is convenient to refer to as palimpsest. In palimpsest drainage, the modern pattern is anomalous with respect to the older; it clearly indicates different topographic and possibly structural conditions at the time of development. 1972 D. J. P. Swift et al. Shelf Sediment Transport xxiii. 499 The floor of the central and southern Atlantic shelf is a palimpsest or multiple imprint surface.

Hence ˈpalimpsest v. trans., to make into a palimpsest, to write anew on (parchment, etc.) after erasure of the original writing; palimpˈsestic a., that is, or that makes, a palimpsest.

1823 New Monthly Mag. VIII. 13 Discoveries‥of Palimpsestic parchments had not yet furnished fresh matter for research. 1836 F. Mahony Rel. Father Prout, Songs Horace i. (1859) 376 Thy MSS. have come down to us unmutilated by the pumicestone of palimpsestic monk. 1900 Expositor June 420 We may wonder less at this Sinaitic‥codex having been palimpsested.