Pal"imp*sest (?), n. [L. palimpsestus, Gr. &?; scratched or scraped again, &?; a palimpsest; &?; again + &?; to rub, rub away: cf. F. palimpseste.] A parchment which has been written upon twice, the first writing having been erased to make place for the second. Longfellow.

• A manuscript or document that has been erased or scraped clean, for reuse of the paper, parchment, vellum, or other medium on which it was written. Many historical texts have been recovered using ultraviolet light and other technologies to read the erased writing.
       
• 2006: Cory Doctorow, "Correcting the Record: Wikipedia vs The Register" in http://www.boingboing.net/2006/01/11/correcting_the_recor.html - Wikipedia's History and Discuss pages are palimpsests recording the process by which the truth was eventually negotiated.
  
• (astronomy) circular features believed to be lunar craters that have been obliterated by later volcanic activity
  
• geological features thought to be related to features or effects below the surface
  
• (computing) memory that has been erased and re-written
  
• To scrape clean, as in parchment, for reuse
  
• On paper: to reuse, often by erasure or change of pen direction or color. Especially fueled by Earth Day.
       Typically refers to a multi-layered work, e.g. new ads covering old on a roadside sign