DICHOTOMY

noun (plural -mies) Etymology: Greek dichotomia, from dichotomos Date: 1610 a division into two especially mutually exclusive or contradictory groups or entities , the phase of the moon or an inferior planet in which half its disk appears illuminated, 3. bifurcation , a system of branching in which the main axis forks repeatedly into two branches, branching of an ancestral line into two equal diverging branches, something with seemingly contradictory qualities