The Collaborative International Dictionary of English v.0.48:

Sneezing \Sneez"ing\, n. (Physiol.)
   The act of violently forcing air out through the nasal
   passages while the cavity of the mouth is shut off from the
   pharynx by the approximation of the soft palate and the base
   of the tongue.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Sneeze \Sneeze\, v. i. [imp. & p. p. Sneezed; p. pr. & vb. n.
   Sneezing.] [OE. snesen; of uncertain origin; cf. D. snuse
   to sniff, E. neese, and AS. fne['o]san.]
   To emit air, chiefly through the nose, audibly and violently,
   by a kind of involuntary convulsive force, occasioned by
   irritation of the inner membrane of the nose.
   [1913 Webster]

   Not to be sneezed at, not to be despised or contemned; not
      to be treated lightly. [Colloq.] "He had to do with old
      women who were not to be sneezed at." --Prof. Wilson.
      [1913 Webster]

WordNet (r) 3.0 (2006):

sneezing
    n 1: a symptom consisting of the involuntary expulsion of air
         from the nose [syn: sneeze, sneezing, sternutation]