瀉

A phono-semantic compound consisting of:

水 (water) — semantic component, indicating liquid or flow;

寫 (to copy; xiě) — phonetic component, providing the sound (사 / xiè). The structure conveys liquid being poured or released, extending naturally to meanings like “to spill” or “to discharge.”
Semantic development: - water flowing out; - pouring or spilling liquid; - discharging from the body; - diarrhea (medical sense). The meaning extends from physical flow to biological discharge.

In Korean, 瀉 appears mainly in medical or formal contexts.

사하 (瀉下) — purgation; to induce bowel movement

토사 (吐瀉) — vomiting and diarrhea

The medical meaning “diarrhea” comes from the idea of uncontrolled discharge.

Often used in classical medicine and traditional East Asian medical terminology.

Compared to 泄, which implies leakage, 瀉 suggests a more deliberate or strong outflow. The imagery of water pouring out gives the character a vivid and concrete foundation.
Related characters: 流 — to flow

注 — to pour

洩 — to leak; to discharge

排 — to expel

Among these, 瀉 emphasizes forceful or active release, especially of liquids.