unsurpassable

From un- +‎ surpassable.

unsurpassable (comparative more unsurpassable, superlative most unsurpassable)

1. Not surpassable; unable to be surpassed.

   Synonym: insurpassable

   • 1908 October, Kenneth Grahame, The Wind in the Willows, New York, N.Y.: Charles Scribner’s Sons, →OCLC:

     On either side of them, as they glided onwards, the rich meadow-grass seemed that morning of a freshness and a greenness unsurpassable. Never had they noticed the roses so vivid, the willow-herb so riotous, the meadow-sweet so odorous and pervading.