IPA: /ˈfæstɪst/
KK: /ˈfæstɪst/
The highest speed; quicker than all others.
Usain Bolt is known as the fastest runner in the world.
Comparative: faster
Superlative: fastest
Fastest → It is formed from "fast" (from Old English *fæst*, meaning firm or steadfast) and the suffix "-est" (used to form the superlative degree). The word "fastest" means the most firm or steadfast in terms of speed.
Think of 'fast' meaning firm or steadfast, and remember that 'fastest' refers to being the most firm in speed.