Definitions:
the lowest part or edge of something, especially the part on which it rests or is supported

a conceptual structure or entity on which something draws or depends

a place used as a centre of operations by the armed forces or others; a headquarters

a main or important element or ingredient to which other things are added

a substance capable of reacting with an acid to form a salt and water, or (more broadly) of accepting or neutralizing hydrogen ions.

the middle part of a bipolar transistor, separating the emitter from the collector.

the root or stem of a word or a derivative.

a number used as the basis of a numeration scale.

each of the four stations that must be reached in turn to score a run.

use (something specified) as the foundation or starting point for something

situate at a specified place as the centre of operations

without moral principles; ignoble

denoting or befitting a person of low social class.

(of coins or other articles) not made of precious metal