Tropic of Cancer Series: Why Is It That The Letter X Represents ‘The Unknown’

Tropic of Cancer Series: What’s the dark horse story of the 24th letter of English alphabets? According to, “the Romans took the /x/ sound from one alphabet (Chalcidian) and combined it with the Chi symbol from another alphabet (Greek) and thus X was born”. May be not.

“The unknown” (as Al-shayyin) was worked out in Arabic and in Algebra –in the first few centuries of the Common Era (CE) by the Persians, the Arabs and the Turks,” says Terry Moore in a TED lecture dated 2012. “Algebra traveled north (to Spain) 1100 years later in the 11th and 12th century…the unknown thing (al-shayyin) became X.”