Expectorant: A medication that helps bring up mucus and other material from the lungs, bronchi, and trachea. An example of as expectorant is guaifenesin 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. From the Latin expectorare, to expel from the chest, from ex-, out of + pectus, chest.