To save you time I checked up the definition of "definition" (Wordnik dictionary)

1. A statement of the meaning of a word, phrase, or term, as in a dictionary entry.

2. A statement or description of the fundamental character or scope of something.

3. The act or process of stating a precise meaning or significance; formulation of a meaning.

So, it could be the definition of insanity. Just not the dictionary definition. YW.

Then why say “the definition of” when it should actually be “a symptom of”? That’s what bothers me about this phrase. It sounds intellectual but it doesn’t hold up under scrutiny.