synovial fluid vs secretion

synovial fluid and secretion both are nouns.

Word	Noun	Adjective	Verb	Adverb
synovial fluid	Yes	No	No	No
secretion	Yes	No	No	No

As nouns, secretion is a hypernym of synovial fluid; that is, secretion is a word with a broader meaning than synovial fluid:

synovial fluid: viscid lubricating fluid secreted by the membrane lining joints and tendon sheaths etc.
secretion: a functionally specialized substance (especially one that is not a waste) released from a gland or cell

synovial fluid (noun)	secretion (noun)
viscid lubricating fluid secreted by the membrane lining joints and tendon sheaths etc.	a functionally specialized substance (especially one that is not a waste) released from a gland or cell
	the organic process of synthesizing and releasing some substance