army corps vs WAC

army corps and WAC both are nouns.

Word	Noun	Adjective	Verb	Adverb
army corps	Yes	No	No	No
WAC	Yes	No	No	No

As nouns, WAC is a hyponym of army corps; that is, WAC is a word with a more specific, narrower meaning than army corps:

army corps: an army unit usually consisting of two or more divisions and their support
WAC: an army corps that was organized in World War II but is no longer a separate branch of the United States Army

Other hyponyms of army corps include Women's Army Corps, Reserve Officers Training Corps, ROTC.

army corps (noun)	WAC (noun)
an army unit usually consisting of two or more divisions and their support	an army corps that was organized in World War II but is no longer a separate branch of the United States Army