A crossword is a word puzzle made of white and black squares arranged in a grid, where you fill in words based on clues. Each word runs either across (horizontally) or down (vertically), and the words intersect, sharing letters at certain squares. If “TREE” goes across and “ROSE” goes down, they might share the letter “R” where they cross.

Crossword puzzles first appeared in newspapers in 1913 and quickly became one of the world's most popular word games. To solve a crossword, you read numbered clues like “A large body of water (5 letters)” and write your answer, OCEAN, in the corresponding numbered squares. The tricky part is that each letter you write helps you solve the crossing words too. If you're stuck on one clue, solving a word that crosses it gives you helpful letters to work with.

Crosswords range from simple to fiendishly difficult. Some use straightforward definitions, while others use puns, wordplay, or clever misdirection. The New York Times crossword, for example, gets progressively harder throughout the week, with Monday being easiest and Saturday being brutally challenging. Solving crosswords regularly builds vocabulary, improves spelling, and sharpens your ability to think about words from different angles.