IPA: /ˈbɪziəst/
KK: /ˈbɪziɪst/
The most active or full of activity compared to others.
This is the busiest time of year for the store, with many customers shopping for the holidays.
Comparative: busier
Superlative: busiest
Busiest → It is formed from "busy" (from Old English "bisig", meaning active or engaged) and the suffix "-est" (meaning the most). The word "busiest" means the most active or engaged among others.
Think of someone who is the "most active" or "most engaged" — that's what busiest means.