In his book Beyond Language (Scribner's, 1967), Dmitri Borgmann introduces the concept of difference words. As he points out in Problem 45 (The New Chemistry), the letters of the generating word FORM occupy positions 6, 15, 18 and 13 in the alphabet. The difference between 6 and 15 is 9; between 15 and 18, 3; and between 18 and 13, 5. The letters of the word ICE occupy positions 9, 3 and 5 in the alphabet. Therefore, ICE is called the difference word of FORM. For most words, of course, this process leads to a meaningless jumble of letters instead of a difference word.
Eckler, A. Ross
Word Ways: Vol. 4
, Article 5.
Available at: http://digitalcommons.butler.edu/wordways/vol4/iss3/5