1. Promoting or facilitating the secretion or expulsion of phlegm, mucus, or other matter from the respiratory tract.
2. A medication that helps bring up mucus and other material from the lungs, bronchi, and trachea.

An example of an expectorant is guaifenesin (expectorant drug used to thin mucus and sputum) which promotes drainage of mucus from the lungs by thinning the mucus and also lubricates the irritated respiratory tract.

Sometimes the term expectorant is incorrectly extended to any cough medicine. It comes from the Latin expectorare, "to expel from the chest"; from ex-, "out of" + pectus, "chest".