Why is the ninth month called September?
1864, of chemicals, 1899, of chromosomes, from bi- + -valent, from Latin valentem, present participle of valere "be worth" (see valiant).
bivalent bi·va·lent (bī-vā'lənt)adj.
Having a valence of 2; divalent.
Consisting of a pair of homologous, synapsed chromosomes, as occurs during meiosis; double.