From The Collaborative International Dictionary of English v.0.48 :
Menstruation \Men`stru*a"tion\, n.
The discharge of the menses; also, the state or the period of
menstruating.
[1913 Webster]
From WordNet (r) 3.0 (2006) :
menstruation
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]