IPA: //ˈpiːsfələr//
KK: /ˈpisfələr/
More calm and free from disturbance than something else.
The garden is peacefuller than the busy street outside.
Comparative: peacefuller
Superlative: most peaceful
Peacefuller → It is formed from "peace" (from Old French *pais*, meaning tranquility or absence of conflict) and "-ful" (meaning full of) and "-er" (indicating a comparative form). The word "peacefuller" means more full of peace or more tranquil than something else.
Think of 'peace' as a state of tranquility, and remember that 'peacefuller' means more full of that tranquility.
No commonly confused words.