tendosynovitis vs synovitis

tendosynovitis and synovitis both are nouns.

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

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

tendosynovitis: inflammation of a tendon and its enveloping sheath
synovitis: inflammation of the synovial membrane that lines a synovial joint; results in pain and swelling

Other hypernyms of tendosynovitis include tendinitis, tendonitis, tenonitis.

tendosynovitis (noun)	synovitis (noun)
inflammation of a tendon and its enveloping sheath	inflammation of the synovial membrane that lines a synovial joint; results in pain and swelling