burn, faint light
熹 centers on a gentle, subdued light or glow, often associated with warmth or burning. The meanings 'burn' and 'faint light' connect through the idea of a soft, smoldering fire that gives off a dim radiance rather than a bright flame.
熹 combines 喜 (joy, delight) with 灬 (fire). The character likely expresses the idea of a warm, pleasant glow—a fire that brings comfort or joy. The exact historical development is uncertain, but the phono-semantic structure with 喜 suggesting the sound and fire contributing the meaning is plausible.
The top part 喜 means joy, and the bottom 灬 is fire. Imagine a small, joyful campfire that gives off a faint, cozy light—just enough to warm your hands and lift your spirits.
For キ, picture a key glowing with a faint, magical light in the dark: key -> キ, and the key's soft radiance matches the kanji's meaning of a gentle burn.