General incomprehensibility:
* Incomprehensible: This is the most straightforward and common word for something that cannot be understood.
* Unintelligible: Similar to incomprehensible, but often used specifically for speech that is difficult to understand.
More specific meanings:
* Inscrutable: This word suggests a mystery or hidden meaning that is impossible to understand.
* Opaque: This word implies that something is unclear or hidden, like a foggy window.
* Abstruse: This word describes something that is very difficult to understand due to its complexity.
* Obscure: This word implies something is not clear or easily understood, often because it's hidden or forgotten.
* Elusive: This word means that something is difficult to grasp or understand, like a fleeting concept.
The best word to use depends on the specific context and the type of incomprehensibility you want to convey.