hydrarthrosis vs redness

hydrarthrosis and redness both are nouns.

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

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

hydrarthrosis: inflammation and swelling of a movable joint because of excess synovial fluid
redness: a response of body tissues to injury or irritation; characterized by pain and swelling and redness and heat

Other hypernyms of hydrarthrosis include inflammation, rubor.

hydrarthrosis (noun)	redness (noun)
inflammation and swelling of a movable joint because of excess synovial fluid	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