IPA: /ˈfɪtɪst/
KK: /ˈfɪtɪst/
The best or most suitable for a particular purpose or situation, especially in terms of health or physical condition.
In the competition, only the fittest animals survived the harsh winter.
Fittest → It is formed from "fit" (from Old English *fitt*, meaning suitable or proper) and the suffix "-est" (meaning most). The word "fittest" refers to the most suitable or proper among a group.
Think of 'fit' meaning suitable, and remember that 'fittest' means the most suitable or proper in a given context.
No commonly confused words.