zygosphenalhttp://www.oed.com/dictionary/zygosphenal_adj%3Ftab%3Dmeaning_and_usezygosphenal, adj.
First published 1921; not fully revised

zygosphenaladjective

Anatomy and Zoology.
  1. 1854–
    Belonging to or constituting a zygosphene.
    Stressed as zygoˈsphenal.
    1. 1854
      Surfaces to which the zygosphenal surfaces are adapted.
      R. Owen, Structure of Skeleton & Teeth in Orr's Circle of Sciences: Organic Nature vol. I. 197

Originally published as part of the entry for zygosphene, n.

zygosphene, n. was first published in 1921; not fully revised.