sourness vs tartness

sourness and tartness both are nouns.

Word	Noun	Adjective	Verb	Adverb
sourness	Yes	No	No	No
tartness	Yes	No	No	No

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

Other hyponyms of sourness include acerbity, vinegariness, vinegarishness.

As nouns, sourness and tartness are synonyms defined as:

sourness and tartness: the taste experience when vinegar or lemon juice is taken into the mouth

Other synonyms of sourness include sour.

sourness (noun)	tartness (noun)
the property of being acidic	a sharp sour taste
a sullen moody resentful disposition	a rough and bitter manner
the taste experience when vinegar or lemon juice is taken into the mouth	the taste experience when vinegar or lemon juice is taken into the mouth