flag, banner
纛 centers on a large ceremonial flag or banner, especially one used in military or ritual contexts.
纛 combines 毒 (likely phonetic) with 縣 (suspended, hanging), suggesting a hanging banner or flag. The exact historical development is uncertain.
The top 毒 looks like a decorated pole, and the bottom 縣 suggests something suspended. Picture a large banner hanging from a pole.
For トウ, imagine a tall banner waving at the top of a tower: tower -> トウ.