enough, adequate fully, quite
彀 centers on the idea of sufficiency: being enough, adequate, or quite something. The given meanings all point to reaching a satisfactory level.
The exact historical development of 彀 is uncertain. It visually contains 弓 (bow) and elements resembling 殳 (a hand holding a weapon or tool), but the connection to 'enough' is not clearly established.
Imagine drawing a bow (弓) until the string is pulled back enough—just the right tension. The rest of the character looks like a hand checking the draw, confirming it is adequate.
For コウ, picture a bow being drawn to its limit, and the archer says 'co' (like the start of 'cope') when it's enough: 'co' -> コウ.