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]

The Collaborative International Dictionary of English v.0.48:

Sneeze \Sneeze\, n.
   A sudden and violent ejection of air with an audible sound,
   chiefly through the nose.
   [1913 Webster]

WordNet (r) 3.0 (2006):

sneeze
    n 1: a symptom consisting of the involuntary expulsion of air
         from the nose [syn: sneeze, sneezing, sternutation]
    v 1: exhale spasmodically, as when an irritant entered one's
         nose; "Pepper makes me sneeze"