leather, skin, reform, become serious
革 centers on the idea of a raw hide or skin, and by extension the processed material leather. The meanings 'reform' and 'become serious' come from the idea of stripping away the old surface to reveal or create something new, like tanning a hide.
革 is a pictograph of an animal hide stretched out on a frame for drying or tanning. The modern form retains the central hide shape with the top and bottom suggesting the stretching frame.
The top and bottom strokes look like a frame, and the middle part is the hide stretched out. Picture a fresh animal skin being stretched and dried to make leather. The idea of reform comes from the process of transforming raw hide into something new.
For カク, imagine a leather worker using a sharp tool to cut the hide with a quick 'kak' sound: kak -> カク, and the hide is reformed into leather.
revolution
reform; reformation; reorganization
reform; innovation
leather
change; transformation; reform; revolution; revolutionizing; innovation; upheaval
leather shoes; leather boots
leather; hide
cowhide; oxhide
(China's) Cultural Revolution (1966-76)
history; development
leather goods (products)
administrative reform
indigo-dyed leather
strap (to hang onto); hanging strap
time of great change; era of reform
conservatism and progressivism; conservatives and reformists
coriaceous; leathery
IT revolution; information revolution
leather; tanned animal hide; suede
Iranian Revolution (1978)