dim
焞 centers on dimness, specifically a weak or subdued light, like a fire that is not burning brightly.
焞 combines 火 (fire) with 享, which likely contributes the sound. The exact historical development is uncertain, but the character is associated with dim light.
The fire 火 on the left is paired with 享 on the right. Imagine a fire that is barely flickering, its light dim and subdued, as if the flames are struggling to stay alive.
For トン, picture a dim light bulb that makes a soft 'ton' sound when it flickers out: ton -> トン, and the room goes dim.