x

An unknown quantity or unknown value.

Let X represent the forecast traffic flow in 20 years’ time.

To know whether a word X is heterological, we must already know what X means. (By contrast, I can know that the word “subdermatoglyphic” has certain syntactic properties—it is six-syllabled, contains the letter “m”, etc.— without having any idea of its meaning.) This indirectness is fine as long as X already has an assigned meaning, for in that case the meaning of “heterological” is ultimately grounded. But when X is the word “heterological”, then we are trying to define “heterological” in terms of itself. We have a closed circle, and a contradictory one, due to the negation operator in the definition.

A placeholder for an unknown, suppressed or hypothetical name.

The woman known until now as Witness X has been unmasked after a court ruling.

Suppose that Mr and Mrs X have been married for many years.

A surname, used by those who have had their identity or heritage, including their proper ancestral names, erased or forgotten.

Malcolm X

An online social media network, formerly known as Twitter.

Two senior USAid security officials were suspended on Sunday for blocking Doge officials from a restricted area, a day after the agency’s website went offline, and Musk posted to X that USAid was “beyond repair” and needed to be shut down.

The X Window System, a windowing system for bitmap displays commonly used in Unix-like systems.

The twenty-fourth letter of the English alphabet, called ex and written in the Latin script.