c.1400, from medical Latin, from Greek oidema (genitive oidematos) "a swelling tumor," from oidein "to swell," from oidos "tumor, swelling," from PIE *oid- "to swell" (cognates: Latin aemidus "swelling," Armenian aitumn "a swelling," Old Norse eista "testicle," Old English attor "poison" (that which makes the body swell), and the first element in Oedipus).