ardoise

Etymology
From vernacular of Northern France like, possibly from  or  root *, found also in Ardu-enna (the ), a region where slate has been quarried for centuries.

Noun

 * 1) slate (rock)
 * 2) a small, portable chalkboard
 * 3)  an unpaid bill
 * 4) slate (bar tab)

Adjective

 * 1) Similar in color to slate, a dark gray between neutral or blueish