dichotomy

noun dichotomies

1. countable, uncountable A separation or division into two; a distinction that results in such a division. The dichotomy between the private and the public is central to almost two centuries of feminist writing and political struggle; it is, ultimately, what the feminist movement is all about. Although some feminists treat the dichotomy as a universal, trans-historical and trans-cultural feature of human

   Similar: bisection

2. countable, uncountable Such a division involving apparently incompatible or opposite principles; a duality. But we do not try to characterize the top and bottom parts of the brain in terms of a simple dichotomy or set of dichotomies, which was exactly what was done with the existing and well-known division of the brain into two halves: namely the left versus the right, the dominant pop-culture brain story
3. countable, uncountable The division of a class into two disjoint subclasses that are together comprehensive, as the division of human into female and male. But in the fallacy of false dichotomy, not only do the two alternatives fail to be jointly exhaustive, but they are not even likely. As a result, the disjunctive premise is false, or at least probably false.
4. countable, uncountable The division of a genus into two species; a division into two subordinate parts.

   Similar: partition, trichotomy

5. countable, uncountable A phase of the moon when it appears half lit and half dark, for example at the quadratures. The Ides of Januarius indeed, the preceding month, must have fallen on March 1 at midnight, two days before the first dichotomy of the mean new moon of that month, March 3 at midnight.
6. countable, uncountable Division and subdivision; bifurcation, such as that of a stem of a plant or a vein of the body into two parts as it proceeds from its origin; often successive. 1969, J. F. Rigby, Permian Sphenopsids from Antarctica, Geological Survey Professional Paper 613-F, page F-9, In one forked leaf there is a distinct vein dichotomy, and the leaf boundary commences 1.5 mm above the dichotomy.