foolish, stupid, dull, silly
憃 centers on a lack of intelligence or sharpness: being foolish, stupid, dull, or silly. The meanings all point to a slow or dim mental state.
憃 combines 舂 (pounding grain) with 心 (heart/mind), suggesting a mind that is pounded or dulled. The exact historical development is uncertain, but the component combination likely expresses mental slowness.
Picture a heart (心) being pounded like grain (舂) until it becomes dull and slow. A pounded heart leads to foolish, stupid thoughts.
For トウ, imagine a dull person trying to count to ten but getting stuck: toe -> トウ, and their foolish mind can't get past their toes.