That is mystic or mystical which has associated with it some hidden or recondite meaning, especially of a religious kind; as, the mystic Babylon of the Apocalypse.

J. C. Fernald, English Synonyms and Antonyms (1914)

Example sentences

magical Ivan told Rima that Walid was a magical therapist.
mysterious A mysterious spaceship was flying away from Earth.
occult Sami read books on Satanism and the occult.

Popularity over time

Word	1850 → 2019	Trend
mystical		rising
magical		rising
mysterious		rising
mystic		steady
occult		rising
fey		rising

Use in printed books, per decade from 1850 to 2019.

By length

3 letters: fey¹
4 letters: dark¹
6 letters: secret², hidden², mystic², occult², latent², arcane²
7 letters: magical³, obscure², cryptic²
8 letters: profound², esoteric⁴, ethereal⁴, witching², abstruse², numinous
9 letters: enigmatic⁴, sorcerous, recondite³
10 letters: mysterious⁴
11 letters: kabbalistic
12 letters: sortilegious, thaumaturgic

The small number after each word is its number of syllables (secret² = 2 syllables).