su ‧ do ‧ ku /suːˈdəʊkuː $ -ˈdoʊ-/ BrE AmE noun [uncountable and countable]
a game in which you have to write numbers in a large square which is made up of 81 smaller squares. Each line of squares across and down, and each of the nine groups of nine squares, must contain the numbers 1 to 9 once only.