The Collaborative International Dictionary of English v.0.48:

Ward-corn \Ward"-corn`\, n. [Ward + F. corne horn, L. cornu.]
   (O. Eng. Law)
   The duty of keeping watch and ward (see the Note under
   Watch, n., 1) with a horn to be blown upon any occasion of
   surprise. --Burrill.
   [1913 Webster]