Before X Was X: The Dark Horse Story Of The 24th LetterSince its inception, the letter X has struggled to establish its own identity, so it may be no coincidence that X is commonly used to represent the unknown in both language and mathematics. But, how was it created?
Origin of side horse
First recorded in 1930–35
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019