dichotomy (suomeksi)

kahtiajako (s: separation or division into two / logic: division of a class into two disjoint subclasses that are together comprehensive / taxonomy: division into two subordinate parts)
ristiriita (s)
dikotomia (s: biology: bifurcation in a stem or vein)
halkihaarautuminen (s)
puolikuu (s: astronomy: phase of the moon)