Inscrutable (adjective)

1. Difficult or impossible to understand or explain.
2. Not revealing thoughts, feelings, or motives easily.

Origin:

From the latin word 'inscrutabilis', meaning 'unsearchable, unfathomable'.

Examples:

1. He had an inscrutable expression on his face that was impossible to read.
2. The inscrutable nature of the universe continues to elude human understanding.
3. The company's financial dealings were inscrutable and kept secret from the public.
4. His methods were inscrutable and often led to strange results.
5. The inscrutable workings of the human mind still remain a mystery to many.