Citations:heptagraph


 * 2002, Robert Churchhouse, Codes and Ciphers: Julius Caesar, the Enigma, and the Internet (page 3)
 * A polygraph consists of an unspecified number of adjacent letters. A polygraph need not be recognisable as a word in a language but if we are attempting to decipher a message which is expected to be in English and we find the heptagraph MEETING it is much more promising than if we find a heptagraph such as DKRPIGX.