When you cross something, you travel over it — like when you cross the street, after looking both ways and using the crosswalk, of course.
A commercial pilot might cross the continent several times a week, and a boy might cross several back yards on his way to school. Another kind of cross is a written mark, an upended X on a piece of paper. There's also the adjective cross, which describes someone who is extremely cranky. The Latin root word crux means "stake or cross," but its figurative meaning, "trouble or misery," is related to to traditional use of wooden crosses to hang criminals.