noun
circular definition
A definition that uses the term being defined, or a chain of definitions that loops back to the original term. Used in logic, philosophy, and lexicography.
「循環定義」とは、定義しようとする語を定義の中で使ってしまうことです。
A 'circular definition' is when you use the word you are trying to define within the definition itself.
辞書で「A」を調べると「B」とあり、「B」を調べると「A」とあるのは循環定義の一例だ。
Looking up 'A' in a dictionary and finding 'B', then looking up 'B' and finding 'A', is an example of a circular definition.