Dichotomy /dī-ˈkä-tə-mē/ noun

Definition: Dichotomy is a noun referring to a division between two contradictory or mutually exclusive groups, such as good and evil or light and dark.

It can also refer to something with contradictory qualities, such as a mansion furnished with poor-quality furniture. Unfortunately, these first two meanings are easily confused and often are.

A third usage for the word is for the phase of the moon where half its disk is illuminated.

Dichotomy is a multi-purpose word; it has another usage as a synonym for bifurcation, especially repeated bifurcation as in a plant’s stem. It is also often found in companies with the word false. A false dichotomy is a fallacy that occurs when someone is presented with only two choices when others are also available.

Etymology: The word has its origins in the 16th century, deriving via Latin from the Greek dikhotomia ‘‘a cutting in half’, from dikho- ‘in two, apart’ and –tomia ‘cutting.’

In a Sentence

Historians have written many papers on the religion-secular dichotomy.

The candidates in the presidential race are a representation of the dichotomy between the two parties.

There was always an apparent dichotomy between the things he did and what he had promised that he would do.

Synonyms 

Paradox, Contradiction

Antonyms 

Similarity, Agreement