gastritis vs redness

gastritis and redness both are nouns.

Word	Noun	Adjective	Verb	Adverb
gastritis	Yes	No	No	No
redness	Yes	No	No	No

As nouns, redness is a hypernym of gastritis; that is, redness is a word with a broader meaning than gastritis:

gastritis: inflammation of the lining of the stomach; nausea and loss of appetite and discomfort after eating
redness: a response of body tissues to injury or irritation; characterized by pain and swelling and redness and heat

Other hypernyms of gastritis include inflammation, rubor.

gastritis (noun)	redness (noun)
inflammation of the lining of the stomach; nausea and loss of appetite and discomfort after eating	red color or pigment; the chromatic color resembling the hue of blood
	a response of body tissues to injury or irritation; characterized by pain and swelling and redness and heat