stupid, simple, simple-minded
戇 centers on a lack of intelligence or sophistication: being stupid, simple, or simple-minded. The meanings describe a person whose thinking is unsophisticated or foolish.
戇 combines 贛 (likely phonetic) with 心 (heart/mind) to express a foolish or simple mind. The exact historical development is uncertain.
The top part 贛 looks complex and tangled, like a confused mind, while the bottom 心 shows the heart. Together they suggest a heart full of tangled, simple thoughts: stupidity.
For トウ, imagine a simple-minded person trying to count toes: 'toe' -> トウ, and they get confused counting their own toes.