The Collaborative International Dictionary of English v.0.48:

Menses \Men"ses\, n. pl. [L. mensis month, pl. menses months,
   and the monthly courses of women. Cf. Month.] (Med.)
   The catamenial or menstrual discharge, a periodic flow of
   blood or bloody fluid from the uterus or female generative
   organs.
   [1913 Webster]

WordNet (r) 3.0 (2006):

menses
    n 1: the monthly discharge of blood from the uterus of
         nonpregnant women from puberty to menopause; "the women
         were sickly and subject to excessive menstruation"; "a
         woman does not take the gout unless her menses be stopped"
         --Hippocrates; "the semen begins to appear in males and to
         be emitted at the same time of life that the catamenia
         begin to flow in females"--Aristotle [syn: menstruation,
         menses, menstruum, catamenia, period, flow]