lentivirusPronunciation: /ˈlɛntɪˌvʌɪrəs/Definition of lentivirus noun Medicine any of a group of retroviruses producing illnesses characterized by a delay in the onset of symptoms after infection. Origin: 1970s: from Latin lentus 'slow' + viruslentivirus in other Oxford dictionaries Definition of lentivirus in the US English dictionary