domain vs academia

domain and academia both are nouns.

Word	Noun	Adjective	Verb	Adverb
domain	Yes	No	No	No
academia	Yes	No	No	No

As nouns, academia is a hyponym of domain; that is, academia is a word with a more specific, narrower meaning than domain:

domain: people in general; especially a distinctive group of people with some shared interest
academia: the academic world

Other hyponyms of domain include academe, Grub Street.

domain (noun)	academia (noun)
the content of a particular field of knowledge	the academic world
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