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]

WordNet (r) 3.0 (2006):

coughing
    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]