juvenalostim
considerably
ambidextrous
There is no twelve letter word spelled with the letters 'ntrarxetisan'.
There isn't a twelve letter word, but if you add another letter "n" you get: entertain met (add letter "n") entertainment
battlefields
You are asking us to construct a seven letter word, using twelve letters. This does not seem to be mathematically possible.
There are no twelve letter words that can be spelled with the letters 'jjbndapicite'.
0.083333 repeating
Twelve in Roman numerals is represented as "XII," which consists of three letters. However, if you are looking for a representation using only two letters, you can use "X" for ten and "II" for two, but it still requires three letters. There is no valid two-letter representation for the number twelve in Roman numerals.
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There are no elements which begin with the letter 'P' which have thirteen letters in their name. Praseodymium and Protoactinium each have twelve letters and they are the longest element names begining with the letter 'P.'
There are twelve possible solutions using the rule you stated.