lieutenant junior grade vs lieutenant JG

lieutenant junior grade and lieutenant JG both are nouns.

Word	Noun	Adjective	Verb	Adverb
lieutenant junior grade	Yes	No	No	No
lieutenant JG	Yes	No	No	No

As nouns, lieutenant junior grade and lieutenant JG are synonyms defined as:

lieutenant junior grade and lieutenant JG: an officer holding a commissioned rank in the United States Navy or United States Coast Guard; below lieutenant and above ensign

lieutenant junior grade (noun)	lieutenant JG (noun)
an officer holding a commissioned rank in the United States Navy or United States Coast Guard; below lieutenant and above ensign	an officer holding a commissioned rank in the United States Navy or United States Coast Guard; below lieutenant and above ensign