HQ vs guardhouse

HQ and guardhouse both are nouns.

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

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

HQ: the military installation from which a commander performs the functions of command
guardhouse: a military facility that serves as the headquarters for military police and in which military prisoners can be detained

Other hyponyms of HQ include command post, general headquarters, GHQ.

HQ (noun)	guardhouse (noun)
the military installation from which a commander performs the functions of command	a military facility that serves as the headquarters for military police and in which military prisoners can be detained