If you're thinking of illustration as a visual representation:
* Abstraction: This refers to something that is not concrete or specific, the opposite of a clear and detailed illustration.
* Vague: This describes something that is unclear, ambiguous, or indefinite, the opposite of a precise illustration.
* Non-representational: This term describes art that does not depict recognizable objects or scenes, unlike an illustration.
If you're thinking of illustration as an explanation or example:
* Concealment: This suggests hiding or keeping something secret, the opposite of revealing through illustration.
* Obscurity: This implies being unclear, confusing, or difficult to understand, the opposite of a clear and illustrative explanation.
* Misinterpretation: This refers to understanding something incorrectly, the opposite of a correct and illustrative explanation.
To determine the most accurate antonym, you'll need to consider the specific context in which the word "illustration" is used.