The word Mississippi has a unique pattern of letters. If you were solving a cryptogram puzzle and saw ZVFFVFFVCCV you might guess that the word is Mississippi.
Is the pattern of letters in Mississippi literally unique or just uncommon? What is the shortest word with a unique letter pattern? The longest word?
We can answer these questions by looking at normalized cryptograms, a sort of word signature. These are formed by replacing the first letter in a word with ‘A’, the next unique letter with ‘B’, etc. The normalized cryptogram of Mississippi is ABCCBCCBDDB.
The set of English words is fuzzy, but for my purposes I will take “words” to mean the entries in the dictionary file american-english on my Linux box, removing words that contain apostrophes or triple letters. I computed the cryptogram of each word, then looked for those that only appear once.
Relative to the list of words I used, yes, Mississippi is unique.
The shortest word with a unique cryptogram is eerie. [1]
The longest word with a unique cryptogram is ambidextrously. Every letter in this 14-letter word appears only once.
[1] Update: eerie is a five-letter example, but there are more. Jack Kennedy pointed out amass, llama, and mamma in the comments. I noticed eerie because its cryptogram comes first in alphabetical order.
Besides eerie, I found the 5-letter words amass, llama, and mamma have unique normalized cryptograms.
In /usr/share/dict/words on my Mac, “iiwi” (a Hawaiian bird). has a unique normalized cryptogram. Among five-letter words, I find cooee, reree, llama, oolly, eerie.
amass shares a cryptogram with abaft, baboo, gagee, tutee; mamma shares a cryptogram with cocco, kikki, tatta.
This comment was difficult to type because my Mac wanted to autocorrect many of those words. I think the word list it ships with may be overly permissive.
Been having fun playing with this. In the word list on my Mac, the word “pterygomandibular’ goes one character farther than ‘ambidextrously’ with unique characters, then repeats two. It shows up last in my list of unique cryptograms sorted alphabetically (‘ABCDEFGHIJKLMNOID’).