The Collaborative International Dictionary of English v.0.48:

Billhook \Bill"hook`\, n. [Bill + hook.]
   A thick, heavy knife with a hooked point, used in pruning
   hedges, etc. When it has a short handle, it is sometimes
   called a hand bill; when the handle is long, a hedge bill
   or scimiter.
   [1913 Webster]

WordNet (r) 3.0 (2006):

billhook
    n 1: a long-handled saw with a curved blade; "he used a bill to
         prune branches off of the tree" [syn: bill, billhook]