zygospermhttp://www.oed.com/dictionary/zygosperm_n%3Ftab%3Dmeaning_and_usezygosperm, n.
First published 1921; not fully revised

zygospermnoun

  1. 1880–
    1. 1880
      The conjugated zygospheres..constitute a zygosperm.
      A. W. Bennett & Murray in Quarterly Journal of Microscopical Science vol. XX. 417

Originally published as part of the entry for zygo-, comb. form

zygo-, comb. form was first published in 1921; not fully revised.