"ˌ noun
Etymology: New Latin, from retro- + virus
: any of a family (Retroviridae) of single-stranded RNA viruses (as HIV and 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
• ret·ro·viral "ˌ adjective