one-drop rule

[wuhn-drop rool]

noun

1. U.S. History.,  a social classification, codified in law in some states during the 20th century, that identifies biracial or multiracial individuals as Black if they have any known Black African ancestry, even from a Black ancestor many generations removed.

Word History and Origins

Origin of one-drop rule¹

First recorded in 1920–25 (as one-drop law ); from the ideology that “one drop” of Black African blood made a person Black

Example Sentences

The laws changed over time, and who was categorized as Black often varied by state, but I also discuss the eugenics movement, in which fears about interracial dating and the "degeneracy" of the white race because of interracial dating led to the rise of the "one-drop" rule, and the idea that anyone with any portion of Black blood was considered Black.

Read more on Salon

In the months that followed, Iowa teachers would report curtailing classroom discussions about topics including genocide, sexism, and the “one-drop” rule in response to the new law.

Read more on Washington Post

In seeking a basis for race-based organizing that forged a path between the absurd “one-drop rule” and the false promises of cultural essentialism, Du Bois had distilled centuries of racist pseudoscience, philosophy and law down to an image of the quotidian humiliation of a railway car.

Read more on New York Times

We were no longer living in the Jim Crow era, when race was determined by arbitrary laws such as the one-drop rule, meaning that if a person has any Black DNA at all, they are considered Black.

Read more on Seattle Times

This is like the “one-drop rule” extended to legislation, as other commentators have observed.

Read more on Washington Post