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]