What's the difference between i.e. and e.g.?
1680s, from Hebrew gematriya, from Greek geometria (see geometry). "[E]xplanation of the sense of a word by substituting for it another word, so that the numerical value of the letters constituting either word is identical" [Klein].
the substitution of numbers for letters of the Hebrew alphabet, a favourite method of exegesis used by medieval Kabbalists to derive mystical insights into sacred writings or obtain new interpretations of the texts. Some condemned its use as mere toying with numbers, but others considered it a useful tool, especially when difficult or ambiguous texts otherwise failed to yield satisfactory analysis. Genesis 28:12, for example, relates that in a dream Jacob saw a ladder (Hebrew sullam) stretching from earth to heaven. Since the numerical value of the word sullam is 130 (60 + 30 + 40)-the same numerical value of Sinai (60 + 10 + 50 + 10)-exegetes concluded that the Law revealed to Moses on Mount Sinai is man's means of reaching heaven. Of the 22 letters in the Hebrew alphabet, the first ten are given number values consecutively from one to ten, the next eight from 20 to 90 in intervals of ten, while the final four letters equal 100, 200, 300, and 400, respectively. More complicated methods have been used, such as employing the squares of numbers or making a letter equivalent to its basic value plus all numbers preceding it.