law, commandments, regulations
掟 centers on binding rules: a law, a set of commandments, or formal regulations that must be followed.
掟 combines 扌 (hand) with 定 (determine, fix), suggesting a hand establishing fixed rules or laws.
The hand 扌 beside 定 (determine) shows a hand setting down fixed rules: laws and commandments written in stone.
For トウ, imagine a law being enforced with a loud, sharp tone: tone -> トウ, and the hand enforces the regulation.