This word is acceptable for play in the US & UK dictionaries that are being used in the following games:

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adj. Of, relating to, or being a mystery: mysterious and infinite truths.

adj. Simultaneously arousing wonder and inquisitiveness, and eluding explanation or comprehension: a mysterious visitor; mysterious conduct.

adj. Of unknown origin

adj. Having unknown qualities

adj. Of or pertaining to mystery; containing a mystery; difficult or impossible to understand; inexplicable; obscure; not revealed or explained; enigmatical; incomprehensible.

Partaking of or containing mystery; obscure; not revealed or explained; unintelligible.

Expressing, intimating, or implying a mystery: as, a mysterious look; his manner was very mysterious and important.

adj. having an import not apparent to the senses nor obvious to the intelligence; beyond ordinary understanding

adj. of an obscure nature

"I must frankly admit, however, that, either owing to the derangement of my nerves, or my new impressions in my new lodgings, or my recent melancholy, I gradually began at dusk to sink into that condition which is so common with me now at night in my illness, and which I call mysterious horror."

esoteric    inexplicable    incomprehensible   

mystery   

mysteriously    mysteriousness   

mystic    unintelligible    occult    incomprehensible    inexplicable    dark    secret    enigmatical    obscure    cabalistic   

deleterious    delirious    imperious    serious   

new    terrible    wonderful    magical