The Collaborative International Dictionary of English v.0.48:

Hawk \Hawk\ (h[add]k), n. [OE. hauk (prob. fr. Icel.), havek,
   AS. hafoc, heafoc; akin to D. havik, OHG. habuh, G. habicht,
   Icel. haukr, Sw. h["o]k, Dan. h["o]g, prob. from the root of
   E. heave.] (Zool.)
   One of numerous species and genera of rapacious birds of the
   family Falconid[ae]. They differ from the true falcons in
   lacking the prominent tooth and notch of the bill, and in
   having shorter and less pointed wings. Many are of large size
   and grade into the eagles. Some, as the goshawk, were
   formerly trained like falcons. In a more general sense the
   word is not infrequently applied, also, to true falcons, as
   the sparrow hawk, pigeon hawk, duck hawk, and prairie hawk.
   [1913 Webster]

   Note: Among the common American species are the red-tailed
         hawk (Buteo borealis); the red-shouldered (Buteo
         lineatus); the broad-winged (Buteo Pennsylvanicus);
         the rough-legged (Archibuteo lagopus); the
         sharp-shinned (Accipiter fuscus). See Fishhawk,
         Goshawk, Marsh hawk, under Marsh, Night hawk,
         under Night.
         [1913 Webster]

   Bee hawk (Zool.), the honey buzzard.

   Eagle hawk. See under Eagle.

   Hawk eagle (Zool.), an Asiatic bird of the genus
      Spiz[ae]tus, or Limn[ae]tus, intermediate between the
      hawks and eagles. There are several species.

   Hawk fly (Zool.), a voracious fly of the family
      Asilid[ae]. See Hornet fly, under Hornet.

   Hawk moth. (Zool.) See Hawk moth, in the Vocabulary.

   Hawk owl. (Zool.)
   (a) A northern owl (Surnia ulula) of Europe and America. It
       flies by day, and in some respects resembles the hawks.
   (b) An owl of India (Ninox scutellatus).

   Hawk's bill (Horology), the pawl for the rack, in the
      striking mechanism of a clock.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Surnia ulula
    n 1: grey-and-white diurnal hawk-like owl of northern parts of
         the northern hemisphere [syn: hawk owl, Surnia ulula]