Gematria or gimatria is a system of assigning numerical value to a word or phrase, in the belief that words or phrases with identical numerical values bear some relation to each other, or bear some relation to the number itself as it may apply to a person's age, the calendar year, or the like. The word "gematria" is generally held to derive from Greek ge metri , "geometry", which was used a translation of g ma riy , though some scholars believe it to derive from Greek grammateia, rather; it's possible that both words had an influence on the formation of the Hebrew word. It has been extant in English since the 17th century from translations of works by Giovanni Pico della Mirandola. Although ostensibly derived from Greek, it is largely used in Jewish texts of Tanakh and Talmud, notably in those associated with the Kabbalah. The best-known example of Gematria is the Hebrew word Chai ("life"), which is composed of two letters which add up to 18. This has made 18 a "lucky number" among Jews, and gifts in multiples of $18 are very common among Jews.