Roman numeral

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Any of the numerical symbols formed with the Roman letters I, V, X, L, C, D, and M, representing respectively the numbers 1, 5, 10, 50, 100, 500, and 1,000, used by the ancient Romans and still used today in certain formal contexts.

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

• noun A numeral represented using a Roman system involving the letters I, V, X, L, C, D, and M.
• noun in the plural The system using such letters.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a symbol in the old Roman notation; I,V,X,L,C,D,M represent 1,5,10,50,100,500,1000 respectively in Arabic notation