The Collaborative International Dictionary of English v.0.48:

Cough \Cough\ (k?f), v. i. [imp. & p. p. Coughed (k?ft); p.
   pr. & vb. n. Coughing.] [Cf. D. kuchen, MHG. k?chen to
   breathe, G. keuchen to pant, and E. chincough, the first part
   of which is prob. akin to cough; cf. also E. choke.]
   To expel air, or obstructing or irritating matter, from the
   lungs or air passages, in a noisy and violent manner.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Cough \Cough\, v. t.
   1. To expel from the lungs or air passages by coughing; --
      followed by up; as, to cough up phlegm.
      [1913 Webster]

   2. To bring to a specified state by coughing; as, he coughed
      himself hoarse.
      [1913 Webster]

   To cough down, to silence or put down (an objectionable
      speaker) by simulated coughing.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Cough \Cough\, n. [Cg. D. kuch. See Cough, v. i. ]
   1. 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.
      [1913 Webster]

   2. The more or less frequent repetition of coughing,
      constituting a symptom of disease.
      [1913 Webster]

   Stomach cough, Ear cough, cough due to irritation in the
      stomach or ear.
      [1913 Webster]

WordNet (r) 3.0 (2006):

cough
    n 1: 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 [syn:
         cough, coughing]
    v 1: exhale abruptly, as when one has a chest cold or
         congestion; "The smoker coughs all day"