1.
If you use ~ to describe a book or other piece of writing, you are criticizing it because it is very boring, complicated, or difficult to understand.
For some this is the greatest novel in the world. For others it is ~...
= unintelligible
ADJ disapproval
2.
If a piece of writing is ~, it is impossible to read because the letters are unclear, especially because it has been damaged in some way.
...if contracts are ~ because of the microscopic print...
= illegible
ADJ: usu v-link ADJ
3.
If someone’s face or expression is ~, it is impossible to tell what they are thinking or feeling. (LITERARY)
He looked back at the woman for approval, but her face was ~.
= impenetrable
ADJ