Why "x" Became the Universal Symbol for the Unknown

 

Here's a letter that barely shows up in ordinary English words, yet somehow ended up everywhere else. "x" is the default symbol for an unknown quantity in algebra, shorthand for a kiss at the end of a text, a stand-in for "by" or "cross," and a marker for anything redacted or unnamed. That symbolic reach is wildly out of proportion to how rarely it actually appears in real spelling.

It also has a quietly foundational role in type design specifically: the term "x-height," one of the most fundamental measurements in all of typography, is named directly after this letter. Because "x" has no ascender, descender, or curves to complicate its edges, it's the cleanest possible reference for measuring the height of lowercase letters like "n," "o," and "e."

Structurally, it's about as simple as a letter gets — just two diagonal strokes crossing at a single point, tracing back to a Greek letter used for a combined "ks" sound.

This glyph series breaks down every letter like this. ✍️ #TypeDesign #Typography #FontDesign

Read more: https://letterhanna.com/lowercase-letter-x-design-and-history/