徐

A phono-semantic compound consisting of:

彳 (step radical) — semantic component, associated with walking or movement; 余 (yú) — phonetic component, providing the sound (서 / xú). The combination suggests walking slowly step by step, which naturally developed into meanings like “slow,” “gradual,” and “unhurried.”
Semantic development: - to walk slowly (original image); - slow movement; - gradual progression; - calm, unhurried state. Thus, 徐 evolved from a physical action (slow steps) into an abstract sense of gradual change or calm pace.

서서히 (徐徐히) — gradually; little by little

완서 (緩徐) — slow; gentle

서행 (徐行) — slow driving; proceeding slowly

徐 is widely used as a surname in both China and Korea. The reduplicated form 徐徐 strengthens the sense of gradualness and smooth progression. Often appears in literary descriptions of nature, movement, or time, emphasizing a gentle unfolding rather than abrupt change.
Related characters: 緩 — slow; gentle; relaxed

慢 — slow; sluggish

遲 — late; delayed

步 — step; pace

Among these, 徐 emphasizes controlled, natural slowness, often with a calm or elegant nuance, unlike 慢.