The Collaborative International Dictionary of English v.0.48:

Measles \Mea"sles\, n.; pl. in form, but used as singular in
   senses 1, 2, & 3. [D. mazelen; akin to G. masern, pl., and E.
   mazer, and orig. meaning, little spots. See Mazer.]
   [1913 Webster]
   1. (Med.) A contagious viral febrile disorder commencing with
      catarrhal symptoms, and marked by the appearance on the
      third day of an eruption of distinct red circular spots,
      which coalesce in a crescentic form, are slightly raised
      above the surface, and after the fourth day of the
      eruption gradually decline; rubeola. It is a common
      childhood disease.
      [1913 Webster +PJC]

            Measles commences with the ordinary symptoms of
            fever.                                --Am. Cyc.
      [1913 Webster]

   2. (Veter. Med.) A disease of cattle and swine in which the
      flesh is filled with the embryos of different varieties of
      the tapeworm.
      [1913 Webster]

   3. A disease of trees. [Obs.]
      [1913 Webster]

   4. pl. (Zool.) The larvae of any tapeworm (Taenia) in the
      cysticerus stage, when contained in meat. Called also
      bladder worms.
      [1913 Webster]

   German measles A mild contagious viral disease, which may
      cause birth defects if contracted by a pregnant woman
      during early pregnancy; also called rubella.
      [PJC]