The Collaborative International Dictionary of English v.0.48:

Horse-leech \Horse"-leech`\, n.
   1. (Zool.) A large blood-sucking leech (H[ae]mopsis vorax),
      of Europe and Northern Africa. It attacks the lips and
      mouths of horses.
      [1913 Webster]

   2. A farrier; a veterinary surgeon.
      [1913 Webster]

WordNet (r) 3.0 (2006):

horseleech
    n 1: any of several large freshwater leeches