Mys‐te″ri‐ous (?), a. [F. mystèrieux. See 1st Mystery.] Of or pertaining to mystery; containing a mystery; difficult or impossible to understand; obscure; not revealed or explained; enigmatical; incomprehensible.
God at last
To Satan, first in sin, his doom applied,
Thought in mysterious terms. Milton.
Syn. — Obscure; secret; occult; dark; mystic; cabalistic; enigmatical; unintelligible; incomprehensible.