The Collaborative International Dictionary of English v.0.48:

Harrier \Har"ri*er\ (-[~e]r), n. [From Hare, n.] (Zool.)
   One of a small breed of hounds, used for hunting hares.
   [Written also harier.]
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Harrier \Har"ri*er\, n. [From Harry.]
   1. One who harries.
      [1913 Webster]

   2. (Zool.) One of several species of hawks or buzzards of the
      genus Circus which fly low and harry small animals or
      birds, -- as the European marsh harrier (Circus
      [ae]ruginosus), and the hen harrier (Circus cyaneus).
      [1913 Webster]

   Harrier hawk (Zool.), one of several species of American
      hawks of the genus Micrastur.
      [1913 Webster]

WordNet (r) 3.0 (2006):

harrier
    n 1: a persistent attacker; "the harassers were not members of
         the regular army" [syn: harasser, harrier]
    2: a hound that resembles a foxhound but is smaller; used to
       hunt rabbits
    3: hawks that hunt over meadows and marshes and prey on small
       terrestrial animals