synovitis vs redness

synovitis and redness both are nouns.

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

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

synovitis: inflammation of the synovial membrane that lines a synovial joint; results in pain and swelling
redness: a response of body tissues to injury or irritation; characterized by pain and swelling and redness and heat

Other hypernyms of synovitis include inflammation, rubor.

synovitis (noun)	redness (noun)
inflammation of the synovial membrane that lines a synovial joint; results in pain and swelling	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