Definition of "Ξ"

Those smaller particles are quarks in this case, meaning that the Ξcc++ is a hadron—the generic name for particles made of quarks.

2017 August 20, Jon Butterworth, “Newly discovered particles, and what's in them”, in The Guardian‎ (in English)

Ethereum's currency unit is called ether, identified also as “ETH” or with the symbols Ξ (from the Greek letter “Xi” that looks like a stylized capital E) or, less often, ♦: for example, 1 ether, or 1 ETH, or Ξ1, or ♦1.

2018, Andreas M. Antonopoulos, Gavin Wood, chapter 2, in Mastering Ethereum […] ‎ (in English), O'Reilly Media