1.  horsefly(n = noun.animal) hippobosca equina, horse tick - winged fly parasitic on horses;
is a kind of hippoboscid, louse fly
is a member of genus hippobosca, hippobosca

2.  horsefly(n = noun.animal) cleg, clegg, horse fly - large swift fly the female of which sucks blood of various animals;
is a kind of gadfly
is a member of family tabanidae, tabanidae

1.  Any dipterous fly of the family Tabanidæ, that stings horses, and sucks their blood. [1913 Webster]
" Of these flies there are numerous species, both in Europe and America. They have a large proboscis with four sharp lancets for piercing the skin. Called also breeze fly. See Illust. under Diptera, and Breeze fly." [1913 Webster]

2.  The horse tick or forest fly (Hippobosca). [1913 Webster]

horsefly, n. (pl. -flies) any of various biting dipterous insects of the family Tabanidae troublesome esp. to horses.

horsefly weed