unmatchable

adj

1. Unable to be matched.

   “An edge in a graph which has a perfect matching is an unmatchable edge if no perfect matching in the graph contains that edge.”

2. Uniquely good; not approached by anything else in quality or excellence.

   “Yes, the originals were fantastic, perhaps even unmatchable.”

noun

1. Something that cannot be matched.

   “Both the matchables and the unmatchables direct us along new lines of inquiry. The matchables invite study of kinship, neighbouring, and property as advantageous ladders of social advancement, while the unmatchables invite inquiry into risk, its incidence, and the strategies young people were employing […]”