1
general::
the bottom
the lowest part of something:
• The house is at the bottom of that hill. • She scrolled down to the bottom of the screen.
the underneath/the underside
the bottom surface on the outside of something:
• You will find the serial number on the underneath of the vacuum cleaner.
base
the lowest part or the wide bottom part on which something stands:
• The lamp has a square base. • He had broken a bone at the base of his spine.
the foot
literary the bottom of a tree, a hill, or some stairs:
• There was a small village at the foot of the mountain.
bed
the ground at the bottom of a river, a lake, or the sea:
• the sea bed • They found some interesting stones on the river bed.
the foundations
the layer of cement and stones that forms the bottom of a building:
• The builders have begun laying the foundations for the house.
Longman-Thesaurus