The phrase "most onliest" is not a proper grammatical phrase in English and actually doesn't make sense. However, if we were to break it down into individual words, synonyms for "most" might include "greatest," "ultimate," or "supreme," while synonyms for "onliest" could include "sole," "unique," or "exclusive." To use these words in correct English, we might describe someone as having the "greatest uniqueness" or the "ultimate exclusivity." While these phrases might not be common in everyday language, they could be appropriate in certain situations such as describing a rare and valuable item or highlighting someone's exceptional qualities.