headquarters vs GHQ

headquarters and GHQ both are nouns.

Word	Noun	Adjective	Verb	Adverb
headquarters	Yes	No	No	No
GHQ	Yes	No	No	No

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

headquarters: the military installation from which a commander performs the functions of command
GHQ: military headquarters from which a military commander controls and organizes the forces

Other hyponyms of headquarters include command post, general headquarters, guardhouse.

headquarters (noun)	GHQ (noun)
the military installation from which a commander performs the functions of command	military headquarters from which a military commander controls and organizes the forces
(usually plural) the office that serves as the administrative center of an enterprise
(plural) a military unit consisting of a commander and the headquarters staff