ground forces vs army

ground forces and army both are nouns.

Word	Noun	Adjective	Verb	Adverb
ground forces	Yes	No	No	No
army	Yes	No	No	No

As nouns, ground forces and army are synonyms defined as:

ground forces and army: a permanent organization of the military land forces of a nation or state

Other synonyms of ground forces include regular army.

ground forces (noun)	army (noun)
a permanent organization of the military land forces of a nation or state	a permanent organization of the military land forces of a nation or state
	a large number of people united for some specific purpose