Source : Webster's Revised Unabridged Dictionary (1913)

Tenesmus \Te*nes"mus\, n. [NL., fr. Gr. ?, fr. ? to stretch: cf.
   L. tenesmos.] (Med.)
   An urgent and distressing sensation, as if a discharge from
   the intestines must take place, although none can be
   effected; -- always referred to the lower extremity of the
   rectum.

   {Vesical tenesmus}, a similar sensation as to the evacuation
      of urine, referred to the region of the bladder.

Source : WordNet®

tenesmus
     n : painful spasm of the anal sphincter along with an urgent
         desire to defecate without the significant production of
         feces; associated with irritable bowel syndrome