synovial
Concise Oxford English Dictionary © 2008 Oxford University Press:
synovial /sʌɪˈnəʊvɪəl, sɪ-/
▶adjective relating to or denoting a type of joint which is surrounded by a thick flexible membrane containing a viscous fluid that lubricates the joint.
– origin C18: from mod. L. synovia, prob. formed arbitrarily by the 16th-cent. Swiss physician Paracelsus.
'synovial' also found in these Oxford entries:

