What is the longest word in the English language that utilizes just three unique letters?
All things considered, as indicated by Wikipedia it's:
Evaluates or referrer
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"Long words with only two, three, four, and so forth unmistakable letters incorporate booboo, deeded, muumuu, Teteté (2 particular letters, 6 letters altogether); surveys, referrer (3, 8); pointlessness (4, 13); lack of protection (6, 15); disinterestedness (7, 17); and institutionalisation (8, 20)."