The Collaborative International Dictionary of English v.0.48:

Serous \Se"rous\, a. [Cf. F. s['e]reux. See Serum.] (Physiol.)
   (a) Thin; watery; like serum; as, the serous fluids.
   (b) Of or pertaining to serum; as, the serous glands,
       membranes, layers. See Serum.
       [1913 Webster]

   Serous membrane. (Anat.) See under Membrane.
      [1913 Webster] Serow

WordNet (r) 3.0 (2006):

serous membrane
    n 1: a thin membrane lining the closed cavities of the body; has
         two layers with a space between that is filled with serous
         fluid [syn: serous membrane, serosa]