cough

from The American Heritage® Dictionary of the English Language, 5th Edition.

• intransitive verb To expel air from the lungs suddenly and noisily, often to keep the respiratory passages free of irritating material.
• intransitive verb To make a noise similar to noisy expulsion of air from the lungs.
• intransitive verb To expel by coughing.
• noun The act of coughing.
• noun An illness marked by frequent coughing.

from The Century Dictionary.

• To make a more or less violent effort, accompanied with noise, to expel the air from the respiratory organs, and force out any matter that irritates the air-passages, or renders respiration difficult.
• To expel from the air-passages by a more or less violent effort with noise and usually with expectoration: followed by up: as, to cough up phlegm.
• noun An abrupt and more or less violent and noisy expiration, excited by some irritation of the respiratory organs.
• To lay up for; store as in a coffer.

from the GNU version of the Collaborative International Dictionary of English.

• intransitive verb To expel air, or obstructing or irritating matter, from the lungs or air passages, in a noisy and violent manner.
• transitive verb To expel from the lungs or air passages by coughing; -- followed by up.
• transitive verb To bring to a specified state by coughing.
• transitive verb to silence or put down (an objectionable speaker) by simulated coughing.
• noun A sudden, noisy, and violent expulsion of air from the chest, caused by irritation in the air passages, or by the reflex action of nervous or gastric disorder, etc.
• noun The more or less frequent repetition of coughing, constituting a symptom of disease.
• noun cough due to irritation in the stomach or ear.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• verb To push air from the lungs in a quick, noisy explosion.
• verb To make a noise like a cough
• noun A sudden, usually noisy expulsion of air from the lungs, often involuntary.
• noun A condition that causes one to cough; a tendency to cough.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• verb exhale abruptly, as when one has a chest cold or congestion
• noun a sudden noisy expulsion of air from the lungs that clears the air passages; a common symptom of upper respiratory infection or bronchitis or pneumonia or tuberculosis