knowledge base vs domain

knowledge base and domain both are nouns.

Word	Noun	Adjective	Verb	Adverb
knowledge base	Yes	No	No	No
domain	Yes	No	No	No

As nouns, knowledge base and domain are synonyms defined as:

knowledge base and domain: the content of a particular field of knowledge

Other synonyms of knowledge base include knowledge domain.

knowledge base (noun)	domain (noun)
the content of a particular field of knowledge	the content of a particular field of knowledge
	people in general; especially a distinctive group of people with some shared interest
	(mathematics) the set of values of the independent variable for which a function is defined
	territory over which rule or control is exercised
	a particular environment or walk of life