military group vs military unit

military group and military unit both are nouns.

Word	Noun	Adjective	Verb	Adverb
military group	Yes	No	No	No
military unit	Yes	No	No	No

As nouns, military group and military unit are synonyms defined as:

military group and military unit: a unit that is part of some military service

Other synonyms of military group include force, military force.

military group (noun)	military unit (noun)
a unit that is part of some military service	a unit that is part of some military service