1.
If you describe something as ~, you mean that it cannot be understood or explained, usually because it is very strange or complicated.
For some ~ reason, there are no stairs where there should be...
How odd life was, how ~, how profoundly unjust.
= inexplicable
ADJ
2.
If you use ~ to describe a person or the expression on their face, you mean that you cannot tell what they are thinking or what they intend to do. (LITERARY)
...a strange, ~ and unpredictable individual.
...the dark eyes that right now seemed opaque and ~.
= inscrutable
ADJ