The Collaborative International Dictionary of English v.0.48:

Hen \Hen\, n. [AS. henn, hen, h[ae]n; akin to D. hen, OHG.
   henna, G. henne, Icel. h?na, Dan. h["o]na; the fem.
   corresponding to AS. hana cock, D. haan, OHG. hano, G. hahn,
   Icel. hani, Dan. & Sw. hane. Prob. akin to L. canere to sing,
   and orig. meaning, a singer. Cf. Chanticleer.] (Zool.)
   The female of the domestic fowl; also, the female of grouse,
   pheasants, or any kind of birds; as, the heath hen; the gray
   hen.
   [1913 Webster]

   Note: Used adjectively or in combination to indicate the
         female; as, hen canary, hen eagle, hen turkey, peahen.
         [1913 Webster]

   Hen clam. (Zool.)
   (a) A clam of the Mactra, and allied genera; the sea clam
       or surf clam. See Surf clam.
   (b) A California clam of the genus Pachydesma.

   Hen driver. See Hen harrier (below).

   Hen harrier (Zool.), a hawk (Circus cyaneus), found in
      Europe and America; -- called also dove hawk, henharm,
      henharrow, hen driver, and usually, in America, marsh
      hawk. See Marsh hawk.

   Hen hawk (Zool.), one of several species of large hawks
      which capture hens; esp., the American red-tailed hawk
      (Buteo borealis), the red-shouldered hawk (Buteo
      lineatus), and the goshawk.
      [1913 Webster]

WordNet (r) 3.0 (2006):

hen hawk
    n 1: nontechnical term for any hawks said to prey on poultry
         [syn: chicken hawk, hen hawk]