erythromycin(n = noun.artifact) e-mycin, erythrocin, ethril, ilosone, pediamycin - an antibiotic (trade name Erythrocin or E-Mycin or Ethril or Ilosone or Pediamycin) obtained from the actinomycete Streptomyces erythreus; effective against many Gram-positive bacteria and some Gram-negative;