硬

Phono-semantic compound:

石 (돌 석, “stone, rock”) — semantic component, indicates hardness.

更 (다시 갱 / 고칠 경) — phonetic component.

硬化 (경화) — hardening, sclerosis

硬直 (경직) — rigidity, stiffness

強硬 (강경) — firm, strong, unyielding

硬幣 (경폐) — coin (lit. “hard currency”)

Unlike most characters with phonetic 更, which yield readings with initial g- (경/갱), 硬 has the unusual initial ŋ- sound.

This explains why Korean (경), Japanese (kō), and Chinese (yìng) diverge from the expected geng class readings.