bottom

low

Near the ground, or not high.

down

Towards or in a lower place; from a higher point to a lower one.

under

In or to a lower place than something, or covered by it.

base

The bottom part that something stands on, or the main place a group works from.

floor

The flat part of a room that you walk on and stand on.

bum

The part of your body that you sit on. An informal word.

depth

How deep something is; the distance from the top of water down to the bottom.

underneath

Directly under something, often covered or hidden by it.