synovium vs tissue layer

synovium and tissue layer both are nouns.

Word	Noun	Adjective	Verb	Adverb
synovium	Yes	No	No	No
tissue layer	Yes	No	No	No

As nouns, tissue layer is a hypernym of synovium; that is, tissue layer is a word with a broader meaning than synovium:

synovium: a thin membrane in synovial (freely moving) joints that lines the joint capsule and secretes synovial fluid
tissue layer: a pliable sheet of tissue that covers or lines or connects the organs or cells of animals or plants

Other hypernyms of synovium include membrane.

synovium (noun)	tissue layer (noun)
a thin membrane in synovial (freely moving) joints that lines the joint capsule and secretes synovial fluid	a pliable sheet of tissue that covers or lines or connects the organs or cells of animals or plants