n :  any of a group of RNA-containing viruses (as HIV and the Rous sarcoma virus) that produce reverse transcriptase by means of which DNA is synthesized using their RNA as a template and incorporated into the genome of infected cells and that include numerous tumorigenic viruses - called also RNA tumor virus  ret*ro*vi*ral adj ret*ro*vi*ral*ly adv 
 
 
 
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