This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
蔜 combines the grass radical 艹 with the phonetic component 敖. The exact historical development and original meaning are uncertain.
The top grass radical 艹 suggests a plant, and the bottom 敖 gives a sense of something tall or proud. Picture a tall, proud weed whose name you don't know.
For ゴウ, imagine a proud weed growing tall and saying 'Go!' to the other plants: Go -> ゴウ.