Lewis & Short

planca, ae, f. [root πλακ-; v. 2. plaga], = πλάξ,

  1. I. a board, slab, plank (post-Aug.): plancae tabulae planae, Paul. ex Fest. p. 231 Müll.: roboreae, Pall. 1, 21, 2.
  2. II. A slab of marble, slab upon graves, Inscr. Don. 278, 3; Inscr. Murat. 1427, 4.