The Collaborative International Dictionary of English v.0.48:
Sui generis \Su"i gen"e*ris\ [L.] Of his or its own kind. [1913 Webster]WordNet (r) 3.0 (2006):
sui generis adj 1: constituting a class of its own; unique; "a history book sui generis"; "sui generis works like Mary Chestnut's Civil War diary"