The Collaborative International Dictionary of English v.0.48:

Vertigo \Ver"ti*go\ (?; 277), n.; pl. E. Vertigoes, L.
   Vertigines. [L., fr. vertere to turn. See Verse.]
   1. (Med.) Dizziness or swimming of the head; an affection of
      the head in which objects, though stationary, appear to
      move in various directions, and the person affected finds
      it difficult to maintain an erect posture; giddiness.
      --Quain.
      [1913 Webster]

   2. (Zool.) Any one of numerous species of small land snails
      belonging to the genus Vertigo, having an elongated or
      conical spiral shell and usually teeth in the aperture.
      [1913 Webster]

WordNet (r) 3.0 (2006):

vertigo
    n 1: a reeling sensation; a feeling that you are about to fall
         [syn: dizziness, giddiness, lightheadedness,
         vertigo]