Dictionary.net

A slight, though prolonged, whistling sound, occurring either at the commencement of inspiration, or of expiration, owing to the presence of mucus, thin and viscid, but not abundant, which obstructs, more or less completely, the smaller bronchial ramificatiois. It is seated in the small tubes, and occurs in the first stage of bronchitis. The clicking and whistling varieties differ, in the former being short, the latter prolonged. The former is a quick, sharp sibilus or whistle, which ceases almost in stantaneously; the latter a prolonged sibilus, of less sharpness, lasting almost the whole time of the movement which it accompanies. To these may be added the hissing variety, the name sufficiently indicating its character.