Greek numeral

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun One of the Greek numerals. A symbol formed from one or more of the letters of the Greek alphabet which has been modified by the addition of a mark, thus: Δ' θ'. These are used to numerate monarchs, chapters, etc as Roman numerals are used in English.
• noun One of the words of the Greek language used to represent a number.