central office vs main office

central office and main office both are nouns.

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

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

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

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

central office (noun)	main 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