zygonemahttp://www.oed.com/dictionary/zygonema_n%3Ftab%3Dmeaning_and_usezygonema, n.
First published 1921; not fully revised

zygonemanoun

Cytology.
  1. 1911–
    † a. A chromosome at zygotene; b. = zygotene n.; now rare.
    1. 1911
      The debatable stages of the meiotic prophases in which parasyndesis and its associated phenomena occur—leptonema, zygonema..—have been dealt with by many experienced cytologists.
      Quarterly Journal of Microscopical Science vol. 57 32
    2. 1911
      By the time the zygonema is fairly far advanced we do get appearances not unlike what may occasionally..be found in the condensation of a somatic chromosome.
      Quarterly Journal of Microscopical Science vol. 57 33
    3. 1976
      It is generally known that during zygonema (stages XII–XIV in rat spermatogenesis) the homologous sets of sister chromatid pairs begin to come together and associate with one another.
      Nature 8 April 534/2

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

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