The Collaborative International Dictionary of English v.0.48:

Syphilis \Syph"i*lis\, n. [NL., fr. Syphilus, the name of a
   shepherd in the Latin poem of Fracastoro, "Syphilus, sive
   Morbus Gallicus," which was published in 1530; Gr. ? hog,
   swine + ? dear, loving. The term was introduced into nosology
   by Sauvages.] (Med.)
   The pox, or venereal disease; a chronic, specific, infectious
   disease, usually communicated by sexual intercourse or by
   hereditary transmission, and occurring in three stages known
   as primary, secondary, and tertiary syphilis. See under
   Primary, Secondary, and Tertiary.
   [1913 Webster]

WordNet (r) 3.0 (2006):

syphilis
    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]

Moby Thesaurus II by Grady Ward, 1.0:

39 Moby Thesaurus words for "syphilis":
   French disease, Spanish pox, VD, acquired syphilis,
   balanitis gangrenosa, cerebral tabes, chancre, chancroid, clap,
   claps, climatic bubo, congenital syphilis, constitutional syphilis,
   dose, dose of clap, fifth venereal disease, general paresis,
   gonorrhea, granuloma inguinale, granuloma venereum, great pox,
   hard chancre, latent syphilis, locomotor ataxia, morbus Gallicus,
   paralytic dementia, paresis, pox, pudendal ulcer, simple chancre,
   social disease, soft chancre, syph, syphilitic meningoencephalitis,
   tabes, tabes dorsales, tertiary syphilis, tropical bubo,
   venereal disease