means the steady persistence in doing something difficult despite obstacles, delay, or discouragement.

from From Latin perseverantia, from perseverare 'to persist, continue steadfastly,' built from per- 'thoroughly' plus severus 'strict, serious, severe.' So at its root it's about being thoroughly serious — staying grimly stern in your purpose long after lighter resolve would have wandered off. It reached English through Old French perseverance in the medieval period, keeping that flavor of dogged, unsmiling commitment.