The Collaborative International Dictionary of English v.0.48:

Hoot \Hoot\, n.
   1. A derisive cry or shout. --Glanvill.
      [1913 Webster]

   2. The cry of an owl.
      [1913 Webster]

   3. A very funny event, person, or experience; as, watching
      Jack try to catch that greased pig was a hoot.
      [PJC]

   Hoot owl (Zool.), the barred owl (Syrnium nebulosum). See
      Barred owl.

   not give a hoot not care at all.
      [1913 Webster]

WordNet (r) 3.0 (2006):

hoot owl
    n 1: any owl that hoots as distinct from screeching