bench, stool
凳 centers on a simple seat for one person: a bench or stool, typically without a backrest.
凳 combines 登 (ascend, climb) with 几 (small table), suggesting a raised platform for sitting. The exact historical development is uncertain, but the component combination likely reflects a seat one climbs onto.
The top 登 looks like climbing up, and the bottom 几 is a small table. Picture climbing onto a small table-like seat: that's a stool or bench.
For トウ, imagine a toe-tapping person sitting on a stool: toe -> トウ, and the stool is just high enough for their feet to tap.