party, faction, clique
黨 centers on a group of people united by shared interests or loyalty: a party, faction, or clique.
黨 is the traditional form of 党. It combines 黑 (black) with 尚 (still, yet), which likely contributed the sound. The original meaning may have been a dark or secretive group, later generalized to any faction or party.
The top part (尚) looks like a roof over a mouth, suggesting a group meeting in a hall. The bottom 黑 (black) can be seen as the group's unified, dark-suited appearance. Together, they form a political party or faction.
For トウ, imagine a political party meeting in a tall tower: tower -> トウ, and the party members gather inside.