The Collaborative International Dictionary of English v.0.48:

oedema \oe*de"ma\, n. [NL., from Gr. ? a swelling, tumor, fr. ?
   to swell.] (Med.)
   A swelling from effusion of watery fluid in the cellular
   tissue beneath the skin or mucous membrance; dropsy of the
   subcutaneous cellular tissue. [Written also edema.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

oedema
    n 1: swelling from excessive accumulation of watery fluid in
         cells, tissues, or serous cavities [syn: edema, oedema,
         hydrops, dropsy]