The Collaborative International Dictionary of English v.0.48:

Micturition \Mic`tu*ri"tion\, n. [L. micturire to desire to make
   water, v. desid. fr. mingere, mictum, to make water.]
   The act of voiding urine; urination; also, a morbidly
   frequent passing of the urine, in consequence of disease.
   [1913 Webster]

WordNet (r) 3.0 (2006):

micturition
    n 1: the discharge of urine [syn: micturition, urination]