TSUMUGU · B2 (est.) · 字
肅
肅 ＝ 聿 ＋ 淵
ㄙㄨˋ · sù
adj — solemn, grave; to clear, purge
字源 FORM — what the parts do
聿義a hand gripping a brush
淵義the deep pool below — the pattern under the hand
A hand holding the brush (聿) at work directly over a deep abyss (淵) — one slip and you're in. Doing the task that carefully makes the bearing grave and exact: 嚴肅、肅靜、肅清. The old graph carries two tellings: this brush-over-the-deep 會意, or 聿 over 肀 sù, which lends the sound.
故事 STORY — a scene to remember it by
手執著筆（聿），就懸在深淵（淵）上方寫字——半點都不敢晃。
The hand grips the brush (聿) and works right above the deep pool (淵) — not daring to waver a hair.
字源記憶法
意 · Meanings
(本義)振敬、嚴— grave, reverent, careful
→嚴肅、肅靜— solemn; hushed and grave常用
⇒肅清— to purge, clear out
(本義) original meaning · → ⇒ each arrow = one more step of extension
關 · Related
聿yù肅 wraps the brush 聿 around the deep-water pattern; bare 聿 is just the brush