non-conjunction
/ˌnɒnkənˈdʒʌŋ(k)ʃn/noun
1 Genetics and Cell Biol. The failure of homologous chromosomes to pair at meiosis.
2 Logic. The relation of the terms in a proposition asserting the negative of a conjunctive proposition (‘not both——and——’).
Origin
Late 17th century (in an earlier sense). From non- + conjunction.