A1 the lowest part of something: Click on the icon at the bottom of the page.
A2 the flat surface on the lowest side of something: There was a price tag on the bottom of the box. Something is stuck to the bottom of my shoe.
A2 [no plural] the lowest position in a group or organization: His team are at the bottom of the first division. B1 [no plural] the ground under a river, lake, or sea: The ship sank to the bottom of the sea.
B1 the part of your body that you sit on
B1 [no plural] the part of an area that is furthest from where you are: the bottom of the garden