United States Marines vs USMC

United States Marines and USMC both are nouns.

Word	Noun	Adjective	Verb	Adverb
United States Marines	Yes	No	No	No
USMC	Yes	No	No	No

As nouns, United States Marines and USMC are synonyms defined as:

United States Marines and USMC: an amphibious division of the United States Navy

Other synonyms of United States Marines include Marine Corps, Marines, United States Marine Corps, US Marine Corps.

United States Marines (noun)	USMC (noun)
an amphibious division of the United States Navy	an amphibious division of the United States Navy