ruggedness vs hardness

ruggedness and hardness both are nouns.

Word	Noun	Adjective	Verb	Adverb
ruggedness	Yes	No	No	No
hardness	Yes	No	No	No

As nouns, ruggedness and hardness are synonyms defined as:

ruggedness (noun)	hardness (noun)
the property of being big and strong	a quality of water that contains dissolved mineral salts that prevent soap from lathering
the quality of being topologically uneven	the property of being rigid and resistant to pressure; not easily scratched; measured on Mohs scale
the quality of being difficult to do	the quality of being difficult to do
	devoid of passion or feeling; hardheartedness
	excessive sternness