HQ vs GHQ

HQ and GHQ both are nouns.

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

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

HQ: 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 HQ include command post, general headquarters, guardhouse.

HQ (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