When the word bias was first used in English in the early-to-mid sixteenth century, it referred to diagonal lines or hypotenuses. Around 1560, it became a technical term in lawn bowls for a type of ball that was heavier on one side, and thus veered off to one side when it was cast. Within a couple decades, the word took on the modern, figurative meaning of "prejudiced belief" and quickly surpassed the previous definitions. Bias was borrowed from the French word biais, which meant "slope" or "slant". That has a debated etymology, but probably comes, through Occitan, from the Proto-Indo-European reconstruction sker, meaning "to cut". The earliest attested use of bias in a statistical context is from 1900 and, according to Google NGram Viewer, literary usage of the word peaked in the year 1995.
Hello! I'm Adam Aleksic, a sophomore studying government and linguistics at Harvard University, where I co-founded the Harvard Undergraduate Linguistics Society. In addition to etymology, I also really enjoy politics, vexillology, geography, board games, conlanging, and law.