U. S. Coast Guard vs coastguard

U. S. Coast Guard and coastguard both are nouns.

Word	Noun	Adjective	Verb	Adverb
U. S. Coast Guard	Yes	No	No	No
coastguard	Yes	No	No	No

As nouns, coastguard is a hypernym of U. S. Coast Guard; that is, coastguard is a word with a broader meaning than U. S. Coast Guard:

U. S. Coast Guard: an agency of the Department of Transportation responsible for patrolling shores and facilitating nautical commerce
coastguard: a military service responsible for the safety of maritime traffic in coastal waters

Other hypernyms of U. S. Coast Guard include agency, authority, bureau, federal agency, government agency, office.

U. S. Coast Guard (noun)	coastguard (noun)
an agency of the Department of Transportation responsible for patrolling shores and facilitating nautical commerce	a military service responsible for the safety of maritime traffic in coastal waters