The Collaborative International Dictionary of English v.0.48:

Pox \Pox\, n. [For pocks, OE. pokkes. See Pock. It is plural
   in form but is used as a singular.] (Med.)
   Strictly, a disease by pustules or eruptions of any kind, but
   chiefly or wholly restricted to three or four diseases, --
   the smallpox, the chicken pox, and the vaccine and the
   venereal diseases.
   [1913 Webster]

   Note: Pox, when used without an epithet, as in imprecations,
         formerly signified smallpox; but it now signifies
         syphilis.
         [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Pox \Pox\, v. t. [imp. & p. p. Poxed; p. pr. & vb. n.
   Poxing.]
   To infect with the pox, or syphilis.
   [1913 Webster]

WordNet (r) 3.0 (2006):

pox
    n 1: a common venereal disease caused by the treponema pallidum
         spirochete; symptoms change through progressive stages; can
         be congenital (transmitted through the placenta) [syn:
         syphilis, syph, pox, lues venerea, lues]
    2: a contagious disease characterized by purulent skin eruptions
       that may leave pock marks