**Roman numeral**, any of the symbols used in a system of numerical notation based on the ancient Roman system. The symbols are I, V, X, L, C, D, and M, standing respectively for 1, 5, 10, 50, 100, 500, and 1,000 in the Hindu-Arabic numeral system. A symbol placed after another of equal or greater value adds its value; e.g., II = 2 and LX = 60. A symbol placed before one of greater value subtracts its value; e.g., IV = 4, XL = 40, and CD = 400. A bar placed over a number multiplies its value by 1,000.

**base**, also called **radix**, in mathematics, an arbitrarily chosen whole number greater than 1 in terms of which any number can be expressed as a sum of that base raised to various powers. The decimal number system that is commonly used expresses all numbers in base 10. For example, 354.76 = (3 × 10^{2}) + (5 × 10^{1}) + (4 × 10^{0}) + (7 × 10^{–1}) + (6 × 10^{–2}). The binary system used in computers expresses numbers in base 2. For example, 25 in binary is (1 × 2^{4}) + (1 × 2^{3}) + (0 × 2^{2}) + (0 × 2^{1}) + (1 × 2^{0}) = 16 + 8 + 0 + 0 + 1 = 25. *See also* numerals and numeral systems.

**c**, third letter of the alphabet, corresponding to Semitic *gimel* (which probably derived from an early sign for “camel”) and Greek *gamma* (Γ). A rounded form occurs at Corinth and in the Chalcidic alphabet, and both an angular and a rounded form are found in the early Latin alphabet, as well as in Etruscan. The rounded form survived and became general, and the shape of the letter has since altered little.