ground
畽 centers on ground or land, specifically a plot of earth. The given meaning is simply "ground," so the kanji refers to a piece of land or terrain.
畽 combines 田 (field) with 重 (heavy), likely as a phono-semantic compound where 重 hints at the sound and 田 gives the meaning of ground or land. The exact historical development is uncertain.
A field (田) that is heavy (重) with soil and crops: that's ground, a solid piece of land.
For トン, imagine a ton of heavy ground: ton -> トン, and the field (田) is weighed down by a heavy (重) ton of earth.