counsel, advice, speak out
讜 centers on giving direct, honest counsel: offering advice or speaking out frankly.
讜 combines 言 (speech) with 黨, which likely contributes the sound and may carry a sense of straightforwardness or group opinion. The exact historical development is uncertain.
The speech radical 言 beside the complex 黨 suggests words spoken openly within a group: speaking out with honest advice.
For トウ, imagine a town hall meeting where someone stands to give frank counsel: town -> トウ, and the speech radical 言 marks the spoken advice.