Serous Copy link Serous , adjective [Compare French séreux. See Serum.] (a) (Physiology) Thin; watery; like serum; as, the serous fluids. (b) (Physiology) Of or pertaining to serum; as, the serous glands, membranes, layers. See Serum. Collocations (1) Serous membrane (Anatomy) , See under Membrane.