zygomorphismhttp://www.oed.com/dictionary/zygomorphism_n%3Ftab%3Dmeaning_and_usezygomorphism, n.
First published 1921; not fully revised

zygomorphismnoun

Botany.
  1. 1875–
    The character of being zygomorphic.
    Stressed as zygoˈmorphism.
    1. 1875
      The zygomorphism of the flower.
      A. W. Bennett & W. T. T. Dyer, translation of J. von Sachs, Text-book of Botany 534

Originally published as part of the entry for zygomorphic, adj.

zygomorphic, adj. was first published in 1921; not fully revised.