richness vs overgrowth

richness and overgrowth both are nouns.

Word	Noun	Adjective	Verb	Adverb
richness	Yes	No	No	No
overgrowth	Yes	No	No	No

As nouns, overgrowth is a hyponym of richness; that is, overgrowth is a word with a more specific, narrower meaning than richness:

Other hyponyms of richness include greenness, verdancy, verdure, wilderness.

richness (noun)	overgrowth (noun)
a strong deep vividness of hue	a profusion of growth on or over something else
the property of a sensation that is rich and pleasing	excessive size; usually caused by excessive secretion of growth hormone from the pituitary gland
the property of producing abundantly and sustaining vigorous and luxuriant growth
the property of being extremely abundant
splendid or imposing in size or appearance
the quality of having high intrinsic value
abundant wealth