Double digrams, such as TUTU, serENENess, or drAMAMine, are not paritcularly common in English words; the editor informs me that in Kucera and Francis's Computational Analysis of Present-Day American English they occur, on the average, in less than one word in a thousand in running text . This article gives a type-collection of the 54 different double diagrams found in boldface entries in the Merriam-Webster Pocket Dictionary. It is presented in the form of a quiz for the reader. Only solid double diagrams are permitted; words in which the letter are interrupted by a hyphen or a space, as in retRO-ROcket or GO-GO, don't count. At the end, the reader is invited to supply words containing double diagrams not represented in the Pocket Webster, but in the Webster's Second or Third. A list of double diagrams known to occur in the Air Force list of Webster's Second is given, augmented by a few not there given (such as AIAI in aiaiai, or EHEH in sheheheyanu).
Wheeler, Timothy J.
Word Ways: Vol. 21
, Article 16.
Available at: http://digitalcommons.butler.edu/wordways/vol21/iss4/16