common ground vs footing

common ground and footing both are nouns.

Word	Noun	Adjective	Verb	Adverb
common ground	Yes	No	No	No
footing	Yes	No	No	No

As nouns, footing is a hypernym of common ground; that is, footing is a word with a broader meaning than common ground:

common ground: a basis agreed to by all parties for reaching a mutual understanding
footing: a relation that provides the foundation for something

Other hypernyms of common ground include basis, ground.

common ground (noun)	footing (noun)
a basis agreed to by all parties for reaching a mutual understanding	a place providing support for the foot in standing or climbing
	a relation that provides the foundation for something
	status with respect to the relations between people or groups