The Collaborative International Dictionary of English v.0.48:

Rhonchus \Rhon"chus\, n.; pl. Rhonchi. [L., a snoring, a
   croaking.] (Med.)
   An adventitious whistling or snoring sound heard on
   auscultation of the chest when the air channels are partially
   obstructed. By some writers the term rhonchus is used as
   equivalent to r[^a]le in its widest sense. See R[^a]le.
   [1913 Webster]

WordNet (r) 3.0 (2006):

rhonchus
    n 1: a sound like whistling or snoring that is heard with a
         stethoscope during expiration as air passes through
         obstructed channels