The 1944 Bletchley Park Cryptographic Dictionary

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GOOD :

1. (of code-groups). Occurring or likely to occur a sufficient number of times to be of assistance to the cryptographer.

2. (of difference). Arising from good code-groups.

GOOD DIFFERENCE :

A difference which is equal to, and may be, the difference between two good groups.

GOOD GROUP :

1. A code-group of which the total occurrences amount to more than a given proportion of the material under consideration; a common group.

2. (in a code of which the groups have known limitations). A code group which has the proper limitation and is so known to be not corrupt.

GRAMMATICAL GROUP :

A code group indicating which of the alternative meanings or endings assigned to a particular code group is to be taken.

GREEN :

(of trigrams). Taken from the Heressignaltafel.

GRID :

(in transposition). Used for cage.

GRILLE

(in Transposition).

1. A cage in which certain squares are blacked-out or otherwise marked as not to be used.
2. A perforated card or disc for determining which squares of a cage are to be used or have been used.

GRONSFELD CIPHER :

A letter-substitution cipher system using a numerical key, and therefore characterized by a limitation on the number of ways in which a particular letter can be enciphered, sc. a letter is enciphered either by itself or one of nine other letters.

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