The Collaborative International Dictionary of English v.0.48:

Noseband \Nose"band`\, n.
   That part of the headstall of a bridle which passes over a
   horse's nose.
   [1913 Webster]

WordNet (r) 3.0 (2006):

noseband
    n 1: a strap that is the part of a bridle that goes over the
         animal's nose [syn: noseband, nosepiece]