Meaning of “base” - Learner’s Dictionary

base

noun [ C ] uk us /beɪs/
BOTTOM

B2 the bottom part of something, or the part something rests on:

It's quite easy to fasten the monitor onto the base.
I felt a sharp pain at the base of my thumb.
MAIN PART

the most important part of something, from which other things can develop:

PLACE

B2 the main place where a person lives or works, or from where they do things:

The hotel is a good base for a holiday.
ARMY

B2 a place where people in the army or navy live and work:

an American Air Force base
ORGANIZATION

the place where the main work of an organization is done:

The company's European base is in Frankfurt.
SUBSTANCE

the main substance in a mixture:

paints with an oil base
BASEBALL

one of the four places in baseball that a player must run to in order to win a point

CHEMISTRY

a chemical substance with a pH (= measure of how acid something is) of more than 7

MATHS

a number that is used as the most important unit in a system of counting:

The binary system of counting uses base 2.

(Definition of “base noun” from the Cambridge Learner’s Dictionary © Cambridge University Press)