The word tire has two main meanings:

1. To become weary or lose energy. When you tire during a long hike, your legs get heavy and you need to rest. Athletes tire in the fourth quarter after playing hard all game. Your parents might tire of hearing the same joke repeated fifty times. The adjective tired describes this feeling of exhaustion or being worn out. Something tireless, interestingly, means it never seems to tire: a tireless worker keeps going with steady energy and determination.
2. A thick rubber ring filled with air that fits around a wheel. Car tires, bicycle tires, and truck tires cushion the ride and grip the road. Without tires, vehicles would bump along uncomfortably on hard metal wheels. People often spell this meaning tyre in British English. When a tire goes flat, it loses its air and needs to be pumped back up or replaced.