dichotomy

Concise Oxford English Dictionary © 2008 Oxford University Press:
dichotomy /dʌɪˈkɒtəmi, dɪ-/

▶noun (pl. dichotomies)

• 1 a division or contrast between two things that are opposed or entirely different.

• 2 Botany repeated branching into two equal parts.

– derivatives
dichotomous adjective,
dichotomously adverb.

– origin C16: via mod. L. from Gk dikhotomia, from dikho- ‘in two, apart’ + -tomia (see -tomy).