coldness vs coolness

coldness and coolness both are nouns.

Word	Noun	Adjective	Verb	Adverb
coldness	Yes	No	No	No
coolness	Yes	No	No	No

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

Other hyponyms of coldness include chill, gelidity, iciness, chilliness, nip, frostiness, cool.

As nouns, coldness and coolness are synonyms defined as:

Other synonyms of coldness include chilliness, frigidity, frigidness, iciness.

coldness (noun)	coolness (noun)
the absence of heat	the property of being moderately cold
a lack of affection or enthusiasm	a lack of affection or enthusiasm
the sensation produced by low temperatures	fearless self-possession in the face of danger
	calm and unruffled self-assurance