IPA: /ˈswɪftɪst/
KK: /swɪftɪst/
The fastest or most quick in movement or action.
The cheetah is known as the swiftest animal on land.
Comparative: swifter
Superlative: swiftest
Swiftest → It is formed from "swift" (from Old English *swift*, meaning quick or fast) and the suffix "-est" (meaning the most). The word "swiftest" means the most quick or fast among others.
Think of 'swift' meaning quick, and remember that 'swiftest' refers to the one that is the most quick.
No commonly confused words.