The Collaborative International Dictionary of English v.0.48:

ovulation \o`vu*la"tion\, n. (Physiol.)
   The formation of ova or eggs in the ovary, and the discharge
   of the same. In the human female the discharge occurs about
   halfway between menstruation times.
   [1913 Webster +PJC]

WordNet (r) 3.0 (2006):

ovulation
    n 1: the expulsion of an ovum from the ovary (usually midway in
         the menstrual cycle) [ant: anovulation]