main office vs central office

main office and central office both are nouns.

Word	Noun	Adjective	Verb	Adverb
main office	Yes	No	No	No
central office	Yes	No	No	No

As nouns, main office and central office are synonyms defined as:

main office and central office: (usually plural) the office that serves as the administrative center of an enterprise

Other synonyms of main office include headquarters, home base, home office.

main office (noun)	central office (noun)
(usually plural) the office that serves as the administrative center of an enterprise	(usually plural) the office that serves as the administrative center of an enterprise