A diagonal line is a line that runs from one corner of a shape to another corner, usually at an angle. The term 'diagonal line' can be represented by two different crossword solutions: 'BIAS' (4 letters) and 'SLASH' (5 letters). BIAS is a term used to describe a line that is not straight, but instead has a slight curve or tilt. A SLASH is a punctuation mark that looks like a forward-SLASH (/) and is used to indicate a break in a sentence or to separate words. Both terms can be used to describe a diagonal line.