enigmatic, enigmatical, puzzling
Meaning: not clear to the understanding; "I didn't grasp the meaning of that enigmatic comment until much later"; "prophetic texts so enigmatic that their meaning has been disputed for centuries"
"Pray heaven that the thread may not snap," he repeated, with his enigmatic smile.
Prince Michael smiled his enigmatic, gentle, comprehending smile and caught the coat sleeve of the other.
This scrap of I knew not what, but which had been the occasion of the enigmatic scene I had witnessed at the breakfast-table, necessarily interested me very much and I could not help giving it a look.