Sui generis
Sui generis (; ) is a Latin phrase that means "of its (his, her, their) own kind; in a class by itself; unique."
Sui generis
For example, in road traffic law, a statute may require consideration of large vehicles separately from other vehicles. The word "large" is ambiguous per se, but may be considered "heavy". Thus the relevant legislation (in Australian law) contains a section called "Terms used" or "Definitions" that itemises all words considered ambiguous, and confers specific interpretations consistent with natural language. So, this list tells us that "heavy vehicle" means a vehicle with a "GVM" over 4.5 tons;" and "GVM" means "gross vehicle mass"—the maximum loaded mass of the vehicle. Further explanations cover various contingencies. Thus "large" is equivalent to "heavy" and is (for this unique case) clearly defined, "sui generis".