efavirenz /ɛˈfæv.ɪˌɹɛnz/ noun1 •A nonnucleoside reverse-transcriptase inhibitor C₁₄H₉ClF₃NO₂ that is administered orally with other antiretroviral agents in the treatment of type-1 HIV infection.In generic form, it costs one-eighth as much as efavirenz, the most closely related drug. — 2007