noun, feminine/aʁ.dwaz/plural: ardoises
slate (rock); a small, portable chalkboard; an unpaid bill; slate (bar tab)
From vernacular Late Latin of Northern France like Vulgar Latin *ardēsia, possibly from Gaulish artuā or Gaulish root *ard(u)- (“high, in altitude”), found also in Ardu-enna (the Ardennes), a region where slate has been quarried for centuries.