The Collaborative International Dictionary of English v.0.48:

actinomycin D \actinomycin D\ n. [From actinomyces, the genus of
   the organism in which they were first found.]
   The most well-known of the actinomycins (C62H86N12O16), a
   class of antibiotics which act by binding to DNA and
   inhibiting synthesis of RNA; they act agains gram-positive
   bacteria and many eukaryotic organisma. Actinomycin D has
   been used in human medicine to treat certain tumors.

   Syn: dactinomycin, actinomycin IV, Cosmegen[trade name],
        actinomycin C1, actinomycin I1
        [PJC]