Sui generis
Sui generis (; ) is a Latin phrase that means "of its (his, her, their) own kind; in a class by itself; unique."
Boggart
Boggart is one of numerous related terms used in English folklore for either a household spirit or a malevolent "genius loci" inhabiting fields, marshes or other topographical features. Other names of this group include "bug", "bugbear", "bogey", "bogun", "bogeyman", "bogle", etc., presumably all derived from (or related to) Old English "pūcel", Irish púca and Welsh "bwg" with the same meaning (itself a probable loan from the English "bug").