WordNet sense 1 (beyond what is ordinary or usual; highly unusual or exceptional or remarkable):

extraordinary

WordNet sense 2 (out of the ordinary):

unwonted

WordNet sense 3 (not commonly encountered):

unusual

WordNet sense 4 (not widely known; especially valued for its uncommonness):

rare

WordNet sense 5 (surpassing what is common or usual or expected):

exceptional, special