The Collaborative International Dictionary of English v.0.48:

Morbillous \Mor*bil"lous\, a. [LL. morbilli measles, dim. of L.
   morbus disease: cf. F. morbilleux.]
   Pertaining to the measles; partaking of the nature of
   measels, or resembling the eruptions of that disease; measly.
   [1913 Webster]