Slanting from one corner to the opposite corner, or running at an angle that is neither horizontal nor vertical.
From Greek 'diagonios' where 'dia-' means 'through' and 'gonia' means 'angle.' The word literally describes a line that goes through angles, and was used in geometry since ancient Greek mathematicians.
Diagonal movement fascinates neuroscientists because humans and other animals naturally prefer moving horizontally or vertically—moving diagonally requires more conscious effort and brain coordination, which is why checkers pieces move diagonally as a deliberate game rule.
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