The Collaborative International Dictionary of English v.0.48:

Amenorrhoea \A*men`or*rhoe"a\, Amenorrhea \A*men`or*rhe"a\ \ \
   ([.a]*m[e^]n`[o^]r*r[=e]"[.a]), n. [Gr. 'a priv. + mh`n month
   + "rei^n to flow: cf. F. am['e]norrh['e]e.] (Med.)
   Pathological or physiological absence of menstruation.
   [1913 Webster + AS]

WordNet (r) 3.0 (2006):

amenorrhea
    n 1: absence or suppression of normal menstrual flow [syn:
         amenorrhea, amenorrhoea, amenia]