Other forms: precessions
Precession is when something comes first in a group or list, like the precession of the kids whose last names start with A in your school's graduation ceremony.
You can use this noun as a substitute for precedence, the act of going first in order or time, but it's actually more common as a scientific term meaning "rotating in a wobbly way." The precession of a spinning gyroscope is the usual example a physics teacher gives — a movement that's essentially a rotating object with an axis that's also rotating. In astronomy, precession refers to the changing rotational axis of a planet (or other body).