bad, evil, disaster
慝 centers on moral wrongness and its consequences: badness, evil intent, and the disasters that follow from it.
慝 combines 匿 (conceal, hide) with 心 (heart/mind), suggesting hidden evil or concealed bad intentions. The exact historical development is uncertain, but the component relationship is clear.
A hidden (匿) heart (心) conceals bad intentions, leading to evil acts and eventual disaster.
For トク, imagine a villain hiding a toxic (トク) plan in his heart: toxic -> トク, and the concealed evil brings disaster.