brilliant, shining, bright
炘 centers on intense light and heat: something brilliant, shining, or bright, often associated with fire.
炘 combines 火 (fire) with 斤, which likely contributes the sound. The exact historical development is uncertain, but the fire component clearly relates to brightness and heat.
Fire 火 beside an axe 斤: imagine the axe striking a flint, producing brilliant sparks that shine brightly.
For キン, picture a brilliant king (キング) holding a flaming axe: king -> キン, and the fire makes his crown shine.