IPA: /ˈraʊndəst/
KK: /raʊndɪst/
The most circular in shape or form.
The ball is the roundest object in the room.
Comparative: rounder
Superlative: roundest
Roundest → It is formed from "round" (from Old French *rond*, meaning circular or spherical) and "-est" (a suffix used to form the superlative degree). The word "roundest" means the most circular or spherical in shape.
Think of something being the 'most circular' — 'round' describes the shape, and '-est' indicates the highest degree of that quality.