The Collaborative International Dictionary of English v.0.48:

Horsefly \Horse"fly`\, n.; pl. Horseflies.
   1. (Zool.) Any dipterous fly of the family Tabanid[ae],
      that stings horses, and sucks their blood.
      [1913 Webster]

   Note: 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. (Zool.) The horse tick or forest fly (Hippobosca).
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Breeze \Breeze\, Breeze fly \Breeze" fly`\, n. [OE. brese, AS.
   bri['o]sa; perh. akin to OHG. brimissa, G. breme, bremse, D.
   brems, which are akin to G. brummen to growl, buzz, grumble,
   L. fremere to murmur; cf. G. brausen, Sw. brusa, Dan. bruse,
   to roar, rush.] (Zool.)
   A fly of various species, of the family Tabanid[ae], noted
   for buzzing about animals, and tormenting them by sucking
   their blood; -- called also horsefly, and gadfly. They
   are among the largest of two-winged or dipterous insects. The
   name is also given to different species of botflies. [Written
   also breese and brize.]
   [1913 Webster]