dichotomy

Meanings

1. 1
   noun

   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.

2. 2
   noun

   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.

3. 3
   noun

   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.

From Ancient Greek διχοτομία (dikhotomía, “dichotomy”).

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