sudoku

noun1

1. •
   A type of pencil puzzle played on a square grid, requiring each of the columns, each of the rows, and each of the subregions (called "boxes" or "regions") to contain the lowest whole numbers up to the dimension of the puzzle, usually 1 to 9, once each. The subregions are rectangular or square except in variants.

   • In fact, anything we do just to kill time—even essentially healthy activities like reading, chatting on the phone, or completing a sudoku puzzle—becomes a 'time thief. — 2008