The word "louriest" is spelled with a "u" after the "l" instead of an "o," which may be confusing for English learners. The reason for this spelling difference lies in the word's phonetic transcription. "Lour" is pronounced with a sound like "ow" as in "cow," represented in IPA as /aʊ/, and the suffix "-iest" is pronounced with a short "i" sound as in "sit," represented as /-ɪst/. Therefore, the correct spelling is "louriest" despite its unique appearance.