The Collaborative International Dictionary of English v.0.48:

Prevalent \Prev"a*lent\, a. [L. praevalens, -entis, p. pr. of
   praevalere. See Prevail.]
   1. Gaining advantage or superiority; having superior force,
      influence, or efficacy; prevailing; predominant;
      successful; victorious.
      [1913 Webster]

            Brennus told the Roman embassadors, that prevalent
            arms were as good as any title.       --Sir W.
                                                  Raleigh.
      [1913 Webster]

   2. Most generally received or current; most widely adopted or
      practiced; also, generally or extensively existing;
      widespread; prevailing; as, a prevalent observance;
      prevalent disease.
      [1913 Webster]

            This was the most received and prevalent opinion.
                                                  --Woodward.
      [1913 Webster]

   Syn: Prevailing; predominant; successful; efficacious;
        powerful.

   Usage: Prevalent, Prevailing. What customarily prevails
          is prevalent; as, a prevalent fashion. What actually
          prevails is prevailing; as, the prevailing winds are
          west. Hence, prevailing is the livelier and more
          pointed word, since it represents a thing in action.
          It is sometimes the stronger word, since a thing may
          prevail sufficiently to be called prevalent, and yet
          require greater strength to make it actually
          prevailing.
          [1913 Webster]

WordNet (r) 3.0 (2006):

prevalent
    adj 1: most frequent or common; "prevailing winds" [syn:
           prevailing, prevalent, predominant, dominant,
           rife]