The Collaborative International Dictionary of English v.0.48:

Menstrual \Men"stru*al\, a. [L. menstrualis: cf. F. menstruel.
   See Menstruous.]
   1. Recurring once a month; monthly; gone through in a month;
      as, the menstrual revolution of the moon; pertaining to
      monthly changes; as, the menstrual equation of the sun's
      place.
      [1913 Webster]

   2. Of or pertaining to the menses; as, menstrual discharges;
      the menstrual period.
      [1913 Webster]

   3. Of or pertaining to a menstruum. --Bacon.
      [1913 Webster]

WordNet (r) 3.0 (2006):

menstrual
    adj 1: of or relating to menstruation or the menses; "menstrual
           period" [syn: menstrual, catamenial]

Moby Thesaurus II by Grady Ward, 1.0:

29 Moby Thesaurus words for "menstrual":
   annual, biannual, biennial, bimonthly, biweekly, catamenial,
   centenary, centennial, daily, decennial, diurnal, fortnightly,
   hebdomadal, hourly, momentary, momently, monthly, quarterly,
   quotidian, secular, semestral, semiannual, semimonthly, semiweekly,
   semiyearly, tertian, triennial, weekly, yearly