The Collaborative International Dictionary of English v.0.48:

Synovial \Syn*o"vi*al\, a. [Cf. F. synovial.] (Anat.)
   Of or pertaining to synovia; secreting synovia.
   [1913 Webster]

   Synovial capsule, a closed sac of synovial membrane
      situated between the articular surfaces at diarthrodial
      joints.

   Synovial fluid, synovia.

   Synovial membrane, the dense and very smooth connective
      tissue membrane which secretes synovia and surrounds
      synovial capsules and other synovial cavities.
      [1913 Webster]

WordNet (r) 3.0 (2006):

synovial membrane
    n 1: a thin membrane in synovial (freely moving) joints that
         lines the joint capsule and secretes synovial fluid [syn:
         synovial membrane, synovium]