A logical fallacy in which the definition of a term is more difficult to understand than the term itself. It could be overly complex, or just extremely vague. Thinking of definitions that fit the former is a fun game, but has no place in logical argument

Example: "A thermometer is a device that measures the average kinetic energy of the ambient medium, usually indicating the reading by means of the height of liquid in a narrow vitreous tube."
Example: "A thermometer is this thing that measures stuff."

To prove the fallacy, identify the term and conditions and show that the conditions of definition are no more clear than the term being defined.