headquarters vs ACE

headquarters and ACE both are nouns.

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

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

headquarters: (plural) a military unit consisting of a commander and the headquarters staff
ACE: a major strategic headquarters of NATO; safeguards an area extending from Norway to Turkey

Other hyponyms of headquarters include ACLANT, Allied Command Atlantic, Allied Command Europe.

headquarters (noun)	ACE (noun)
the military installation from which a commander performs the functions of command	a major strategic headquarters of NATO; safeguards an area extending from Norway to Turkey
(usually plural) the office that serves as the administrative center of an enterprise	proteolytic enzyme that converts angiotensin I into angiotensin II
(plural) a military unit consisting of a commander and the headquarters staff