The Collaborative International Dictionary of English v.0.48:

caesarean section \caesarean section\ n. (Surg.),
   the operation of taking a child from the womb by cutting
   through the walls of the abdomen and uterus; -- so called
   because Julius C[ae]sar is reported to have been brought into
   the world by such an operation; -- called also caesarean.

   Syn: cesarean section, cesarian section, caesarean section,
        caesarian section, C-section, cesarean, cesarian.
        [1913 Webster]

WordNet (r) 3.0 (2006):

caesarean section
    n 1: the delivery of a fetus by surgical incision through the
         abdominal wall and uterus (from the belief that Julius
         Caesar was born that way) [syn: cesarean delivery,
         caesarean delivery, caesarian delivery, cesarean
         section, cesarian section, caesarean section,
         caesarian section, C-section, cesarean, cesarian,
         caesarean, caesarian, abdominal delivery]