The term MARK OF A RULER can be broken down into two crossword solutions: INCH (4 letters) and ONEINCH (7 letters). An INCH is a unit of length in the imperial and US customary systems of measurement, equal to 1/12 of a foot. It is also used in other systems of measurement, such as the Japanese system. The term 'oneinch' is often used to refer to a ruler, which is a tool used to measure distances or draw straight lines. A ruler is typically marked with inches, making it a mark of a ruler.