horseflyPronunciation: /ˈhɔːsflʌɪ/Translate horsefly | into French | into German | into Italian | into Spanish Definition of horsefly noun (plural horseflies) a stoutly built fly, the female of which is a bloodsucker and inflicts painful bites on horses, humans, and other large mammals. Family Tabanidae: numerous species, in particular the common European Haematopota pluvialis horsefly in other Oxford dictionaries Definition of horsefly in the US English dictionary