1. Radically distinctive and without equal
   "Bach was unique in his handling of counterpoint";
   - alone, unequaled [US], unequalled [Brit, Cdn], unparalleled, one-of-a-kind
    
2. The single one of its kind
   "the unique existing example of Donne's handwriting"; "a unique copy of an ancient manuscript"; "certain types of problems have unique solutions";
   - singular, one-of-a-kind
    
3. Highly unusual or rare but not the single instance
   "a frankness unique in literature"; "a unique dining experience"; "spoke with a unique accent"; "had unique ability in raising funds"
    
4. (followed by ‘to’) applying exclusively to a given category, condition or locality
   "a species unique to Australia"

See also: incomparable, single, specific, uncomparable, unordinary, unusual

Encyclopedia: Unique