Incomparable means (1) "unequaled" and "matchless" and (2) "incapable of being compared." Uncomparable shares the second of these meanings but not the first."Helen of Troy's beauty was said to have been incomparable." "Bananas and potatoes are uncomparable."
Incomparable is also a term applied to certain words that are considered absolute in meaning and that cannot be used in a comparative or superlative sense. Some students of language have turned incomparable into a noun and list as incomparables such words as UNIQUE. If one says "more unique" or "most unique," what becomes of this word that is used to designate the only one of a kind? If something is perfect, how can it be "more perfect"! A short list of incomparables would contain these words with absolute meaning: eternal, equal, final, total, supreme, infinite, absolute, and fatal.
Dictionary of problem words and expressions. Harry Shaw. 1975.