stiff, hard
硬 centers on physical rigidity: something stiff and hard, resistant to pressure or deformation.
硬 combines 石 (stone) with 更, which likely contributes the sound and reinforces the idea of hardness or rigidity associated with stone.
Stone 石 on the left and 更 on the right: imagine a stone so hard that even trying to change (更) it is impossible. 硬 means stiff and hard like stone.
For コウ, picture a hard stone that makes a loud 'koh!' sound when struck: koh -> コウ, and the stone is stiff and unyielding.
hard; solid; tough
coin
firm; strong; unbending; unyielding; uncompromising; stubborn; tough; hard-line
hardening; vulcanization; vulcanisation; sclerosis; curing
hard (esp. of hardball, tennis, etc.)
stiffening; rigidity; rigor; stiffness; ossification; petrification
hard-liners; diehards; hawks
hardness; solidity
hardness; stiffness
cirrhosis (of the liver)
hard water
pen or pencil
hardness and softness; hard line and moderate line
hardness
hard ball; regulation ball
scratch hardness
atherosclerosis
atherosclerosis
Mohs' hardness
Mohs' hardness