Source : Webster's Revised Unabridged Dictionary (1913)

Siriasis \Si*ri"a*sis\, n. [L., fr. Gr. ???, fr. ??? the Dog
   Star, properly, scorching.] (Med.)
   (a) A sunstroke.
   (b) The act of exposing to a sun bath. [Obs.] Cf.
       {Insolation}.

Source : WordNet®

siriasis
     n : sudden prostration due to exposure to the sun or excessive
         heat [syn: {sunstroke}, {insolation}, {thermic fever}]