In nuclear physics, a barn is a unit of measurement used to describe the cross-sectional areas of reactions for subatomic particles. The name was coined by a group of physicists at Purdue University who were working on the Manhattan Project and needed a secretive-sounding unit equal to 10^−28 square meters. This was considered a large target for particle accelerators, so they joked that reaching it would be "as easy as hitting the side of a barn", hence the name. The word barn has been around since at least the tenth century and is actually a compound of the Old English nouns bere, meaning "barley", and ærn, meaning "place"; barley was one of the most commonly grown grain crops in Anglo-Saxon days. Bere (which is also the source of the word barley if you add the suffix -lic, meaning "like") comes from Proto-Germanic baraz, also meaning "barley", and ærn is from Proto-Germanic razna, meaning "dwelling".
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Hello! I'm Adam Aleksic, a senior studying government and linguistics at Harvard University, where I co-founded the Harvard Undergraduate Linguistics Society. In addition to etymology, I also really enjoy trivia, politics, vexillology, geography, board games, conlanging, art history, and law.