Definition of "Unique" :

adjective: highly unusual or rare but not the single instance

"Spoke with a unique accent."

adjective: radically distinctive and without equal

"Bach was unique in his handling of counterpoint."

adjective: (followed by to') applying exclusively to a given category or condition or locality

"A species unique to Australia."

adjective: the single one of its kind

"The unique existing example of Donne's handwriting."